Demodulation apparatus and receiving apparatus

ABSTRACT

A demodulation apparatus that can support various oscillation frequencies. The portable phone device includes a frequency synthesizer for generating a local-oscillation signal having a local oscillation frequency for converting the frequency of an input receiving signal into an intermediate frequency based on an oscillation signal generated by an TCXO and a synchronization hold portion provided with an NCO for generating a signal having a predetermined frequency based on the oscillation signal generated by TCXO. The frequency synthesizer makes the local oscillation frequency variable by setting the dividing ratio variable in accordance with an arbitrary oscillation frequency so that the intermediate frequency remains within a predetermined range regardless of the oscillation frequency, and an NCO makes the frequency of the signal variable by setting the dividing ratio variable in accordance with the oscillation frequency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. JP2002-053898, filed on Feb. 28, 2002, the disclosure of such applicationbeing herein incorporated by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a demodulation apparatus fordemodulating a predetermined high frequency signal and a signalreceiving apparatus to which the demodulation apparatus is applied,which is capable of calculating the apparatus own position and speedupon receiving signals from a so-called GNSS (Global NavigationSatellites System).

2. Description of the Related Art

In recent years, a GNSS system has become increasingly popular formeasuring position of a moving object on the surface of Earth by usingartificial satellites. Examples of the GNSS system include the GlobalPositioning System (referred to as GPS system below). In the GPS system,a GPS receiver for receiving signals from the GPS satellites has basicfunctions of receiving signals from at least four GPS satellites andcalculating the position of the GPS receiver based on the receivingsignals before reporting to the user.

More specifically, the GPS receiver acquires orbit information of eachGPS satellite by demodulating the signals received from such satellitesand calculates simultaneous equations to determine the three dimensionalposition of such GPS satellite based on the orbit and time informationof each GPS satellite and the delay time of the receiving signals. It isto be noted that the reason why at least four GPS satellites are neededfor obtaining the receiving signals in the GPS system is because thereis a time error between the internal time of the clock equipped with theGPS receiver and an atomic clock with which the GPS satellites areequipped. As a result, pseudo-distances from at least four GPSsatellites are required in order to calculate the four unknownparameters of three dimensional positions and accurate time byeliminating the influence of such errors.

In case of using a consumer purpose GPS receiver in the GPS system,position measurement calculations are performed by receiving from theGPS satellites (Navistar) an L1 band, spread spectrum signal commonlyknown as a C/A (Clear and Acquisition) code.

In the transmission signal known as the L1 band, C/A code has atransmission signal rate, i.e., a chip rate of 1.023 MHz and ismodulated based on a binary phase shift keying modulation system(referred to as BPSK modulation system below) in which a 1575.42 MHzcarrier wave is modulated by a 500 bps data directly spread by apseudo-random noise (PN) family spreading code, e.g., Gold code and thelike having 1023 code length. Since the code length is 1023 in thiscase, the C/A code repeats the spread code of 1023 chips as a period,i.e., 1 period=1 millisecond as shown at the top column in FIG. 14.

The spread code in form of the C/A code is different for each GPSsatellite. However, the spread codes to be used by respective GPSsatellites are predetermined so that the GPS receiver can identify onefrom another. Also, the GPS receiver is designed to recognize when andwhere the signals from the respective GPS satellites can be receivedbased on the navigation message which will be described hereinafter. Asa result, if, e.g., a three dimensional position measurement system isutilized, the GPS receiver receives radio waves from at least four GPSsatellites receivable at any instance and performs spectrum reversespreading and position measurement operations, thereby calculating theown position.

In addition, 1 bit of signal data from each GPS satellite is transmittedat every 20 periods of the spread code, i.e., 20 milliseconds as shownat the second column in FIG. 14. This means that the data transmissionrate is 50 bps as mentioned above. Moreover, 1023 chips which are equalto one period of the spread code are inverted to each other when the bitis “1” or “0”.

Furthermore, 30 bits, i.e., 600 milliseconds of the signal from each GPSsatellite constitutes a word as shown at the third column in FIG. 14. 10words, i.e., 6 seconds of the signal from the GPS satellite constitute a1 sub-frame as shown at the fourth column in FIG. 14. As shown at thefifth column in FIG. 14, inserted into the signal from each GPSsatellite at the top of one sub-frame is a preamble so that apredetermined bit pattern is always included even if the data isrenewed. The data is transmitted subsequent to such preamble.

Finally, 5 sub-frames, i.e., 30 seconds of the signal from each GPSsatellite constitute a frame. And transmitted from each GPS satelliteare the above mentioned navigation messages in the data unit of 1 frame.

The first 3 sub-frames in a frame data are known as Ephemerisinformation which is peculiar to the respective GPS satellites.Contained in the Ephemeris information are parameters for determiningthe orbit of each GPS satellite and the time when the signal is sentfrom the GPS satellite.

All GPS satellites are provided with common time information byutilizing an atomic clock. The time of sending the signal from the GPSsatellite contained in Ephemeris information is in the unit of 1 secondof such atomic clock. It is to be noted that the spread code of the GPSsatellite is generated in synchronism with the atomic clock.

Orbit information contained in Ephemeris information is renewed at everyseveral hours and the same information is used until it is renewed. Forthis end, each GPS satellite has a memory to hold such orbit informationcontained in Ephemeris information, thereby making it possible toaccurately use the same orbit information for several hours. It is to benoted, however, that the time of sending the signal from each GPSsatellite is renewed at every 6 seconds as TOW (Time of Week)information.

On the other hand, the navigation message in the remaining 2 sub-framesin 1 frame data is known as Almanac information which is commonly sentout from all GPS satellites. Such Almanac information requires 25 framesin order to acquire complete information and includes such informationas approximate position information of each GPS satellite andavailability of the GPS satellites. Such Almanac information is renewedat every several days and the same information is used until it isrenewed. As a result, the GPS receiver saves such Almanac information ina memory for accurately using the same information for several days.However, it is to be noted that the GPS satellite may use the sameAlmanac information over several months with slightly lower accuracy.

In order to obtain the above mentioned data by receiving the signal fromthe GPS satellite, the GPS receiver first eliminates the carrier anduses the same spread code as the C/A code used in the GPS satellite thatthe GPS receiver is going to receive for phase synchronizing of the C/Acode in the signal from the GPS satellite, thereby capturing the signalfrom the GPS satellite and performing the spectrum reverse spreading.Upon performing the spectrum reverse spreading by synchronizing in phasewith the C/A code, the GPS receiver detects bits, thereby enabling toacquire the navigation message containing time information based on thesignal from the GPS satellite.

The GPS receiver captures the signal from the GPS satellite byperforming the phase synchronization search of the C/A code. For thephase synchronization search, the GPS receiver detects correlationbetween the spread code generated by the GPS receiver itself and thespread code of the signal received from the GPS satellite. For example,if the correlation value as the result of the correlation detection islarger than a predetermined value, the both are determined to besynchronized. On the other hand, if determined that synchronization isnot established, the GPS receiver controls the phase of the spreadsignal that the GPS receiver generates by any synchronization means soas to synchronize with the spread code of the receiving signal.

It is to be noted that, as described hereinabove, the signal from theGPS satellite is a carrier modulated by a signal of the data beingspread by the spread code based on the BPSK modulation system. As aresult, in order for the GPS receiver to receive the signal from the GPSsatellite, it is necessary to synchronize not only the spread signal butalso to synchronize the carrier and the data. However, synchronizationof the spread signal and the carrier cannot be performed independently.

Also, the GPS receiver in general converts the receiving signal into anintermediate frequency (referred to as IF below) signal by convertingthe carrier frequency of the receiving signal into several MHz or lowerIF frequency. The above mentioned synchronization detection processingis performed on the IF signal. Contained in the carrier of the IF signal(referred to as IF carrier below) are primarily a frequency errorcomponent due to Doppler shift in accordance with the traveling speed ofthe GPS satellite and a frequency error component of a local oscillatorgenerated inside the GPS receiver in case of converting the receivingsignal into the IF signal.

Because the IF carrier frequency is unknown due to these frequency errorfactors, it is necessary to conduct a search for the frequency in theGPS receiver. Also, since the synchronized point (synchronized phase)within 1 period of the spread code is unknown due to dependence to thepositional relationship between the GPS receiver and the GPS satellite,any kind of synchronization technique is required in the GPS receiver asdescribed hereinabove.

Employed synchronization technique in a conventional GPS receiver is acombination of a frequency search on the carrier, a synchronizationcapture by a sliding correlator, a DLL (Delay Locked Loop) and asynchronization hold by a Costas loop. Now, this synchronizationtechnique will be described hereunder.

A clock for driving the spread code generator in the GPS receiver ingeneral uses a reference frequency generator provided in the GPSreceiver after proper dividing. What is used as the reference frequencygenerator is a high precision crystal oscillator. Based on the outputfrom the reference frequency generator, the GPS receiver generates thelocal oscillation signal to be used for converting the receiving signalfrom the GPS receiver into the IF signal.

Now, FIG. 15 shows processing in the frequency search. The GPS receiverconducts the phase synchronization search on the spread code when theclock signal frequency for driving the spread code generator is f1. Inother words, the GPS receiver sequentially shifts the phase of thespread code by 1 chip and detects correlation between the spread codeand the receiving signal from the GPS satellite in each chip phase,thereby detecting the synchronizing phase by detecting the peak ofcorrelation. Also, if the GPS receiver could not find synchronized phasein any phase search for the entire 1023 chips in a clock signalfrequency f1, e.g., the dividing ratio for the reference frequencyoscillator is changed to obtain another clock signal frequency f2, andthe phase search is similarly performed for 1023 chips. The GPS receiverachieves the frequency search by repeating the above operations whilechanging the clock signal frequency in a step manner.

When the GPS receiver detects the clock signal frequency that can besynchronized after conducting such frequency search, the final phasesynchronization of the spread code will be carried out at the clocksignal frequency. Consequently, the GPS receiver can capture the signalfrom the GPS satellite even if the oscillation frequency of the crystaloscillator is shifted.

However, such conventional synchronization technique is not suitable inprinciple for high frequency synchronization. In the GPS receiver, aresponse will be delayed if it takes considerable time forsynchronization of the spread code and the IF carrier, thereby causinginconvenience in actual use. In order to improve such disadvantage, theactual GPS receiver performs parallel processing using a plurality ofchannels, thereby reducing the time required for establishingsynchronization.

On the other hand, techniques for establishing synchronization of thespread spectrum signal at a high speed instead of using the abovedescribed technique by sliding correlation include the use of a matchedfilter. The matched filter can be realized digitally by the use of aso-called transversal filter. Also, the matched filter can realizesynchronization of the spread code at a high speed by utilizing the fastFourier transformation (referred to as FFT below) as a result ofimproved hardware performance in recent years. The latter is based onthe well known high speed correlation calculation technique.

Using such matched filters, if there is a certain correlation, the GPSreceiver can detect the peak of correlation, e.g., as shown in FIG. 16which shows 1 period of the output waveform. The position of the peakindicates the head of the spread code. By detecting the peak, the GPSreceiver can establish synchronization, i.e., detect the phase of thespread code in the receiving signal. Also, the GPS receiver uses thedigital matched filter utilizing, e.g., the above mentioned FFT toperform operation in the frequency range of the FFT, thereby detectingthe phase of the spread code as well as the IF carrier frequency. Then,the GPS receiver converts the phase of the spread code into thepseudo-distance, thereby calculating the position of the GPS receiver incase of detecting at least four GPS satellites. Also, the GPS receivercan calculates the speed of the GPS receiver based on the IF carrierfrequency.

SUMMARY OF THE INVENTION

It is to be noted that, in the GPS receiver utilizing the abovementioned C/A code, it is most likely that a multiple of 1.023 MHz whichis the chip rate of the C/A code is used as the source frequency of theoscillation signal generated by the above mentioned oscillator. Forexample, in case of the GPS receiver using 16.368 MHz, or 16 times ofthe chip rate as the source oscillation frequency, it is typical thatthe operation clock of the digital signal processing portion forprocessing the base band signal is made equal to the frequency of thesource oscillator, or 16.368 MHz. The frequency of the local oscillationsignal used for converting the receiving signal from the GPS satelliteinto the IF signal is equal to 16.368 MHz×96=1571.328 MHz. And the IFsignal frequency is equal to 4.092 MHz. In this case, in the GPSreceiver, if the source oscillation frequency is changed, the IF signalfrequency is largely changed.

For example, if the source oscillation frequency is simply changed from16.368 MHz to 16 MHz in the GPS receiver, the IF signal frequency islargely changed to 39.42 MHz, which is difficult to support in the baseband processing. In another example, if the source oscillation frequencyis changed to 16.4 MHz in the GPS receiver, the IF signal frequencybecomes 1.02 MHz, which can be sufficiently supported in the base bandprocessing. However, if a band pass filter (referred to as BPF below)for down converting has a fixed bandwidth centered at 4.092 MHz, the IFsignal is significantly attenuated.

Also changed in the GPS receiver is the frequency range of NCO (NumericControlled Oscillator) based on the source oscillation frequency to beused for the above mentioned DLL and the Costas loop for demodulatingthe spread spectrum signal and the sampling clock for storing the IFsignal and sampling it at a predetermined sampling frequency.

As described hereinabove, when the source oscillation frequency ischanged in the GPS receiver, it has not been impossible to take measureswhich are adaptive to the base band processing.

In view of that, applications for the GPS receiver include electronicapparatus provided with particular functions such as portable terminalsincluding portable phone devices and the like in which the functions ofsuch GPS receiver are built in. In such case, since an oscillator forgenerating a unique frequency as the clock is installed in theelectronic apparatus, installation of a new oscillator for the GPS unitwhich is a constituting element to achieve the functions of the GPSreceiver accompanied with increased cost and added required space in theelectronic apparatus and source of electromagnetic interference, whichare not desirable from an EMC (Electro Magnetic Compatibility) point ofview.

It is therefore preferable for the electronic apparatus that the clockfor the GPS unit is also acquired from the oscillator installed in theelectronic apparatus. However, since frequencies of the oscillatorsdiffer from one another, it is necessary in the GPS unit that thefrequency converter portion for down converting the receiving signalinto the IF signal and the other digital signal processing portions aredesigned so as to support any oscillation frequency.

These problems are not limited to the functions of the GPS receiver butare common to cases where various units for achieving a function otherthan that of the GPS receiver are assembled or embedded in theelectronic apparatus.

In light of the above problems of the prior art, it is desirable toprovide a demodulation apparatus that can support various oscillationfrequencies and capable of reducing cost and achieving downsizing byutilizing the oscillation frequency from the oscillator alreadyinstalled in the electronic apparatus as the source oscillationfrequency. It is another preferable feature of the present invention toprovide a receiving apparatus applying such demodulation apparatus inwhich another function different from its primary function is assembled.

In order to alleviate the above mentioned problems, a demodulationapparatus for demodulating a high frequency signal, according to apreferred embodiment of the present invention includes: a frequencyconversion means for converting the high frequency signal into anintermediate frequency; a signal processing means for performing asignal processing on an intermediate frequency signal having theintermediate frequency obtained through the frequency conversion means;and a setting means for performing settings on the frequency conversionmeans and the signal processing means; wherein the frequency conversionmeans includes a local oscillation signal generation means forgenerating a local oscillation signal having a local oscillationfrequency for converting a frequency of the high frequency signal intoan intermediate frequency based on a source oscillation signal generatedby a source oscillator and the signal processing means includes a signalgeneration means for sharing the local oscillation signal generatormeans and the source oscillator and for generating a signal having apredetermined frequency based on the source oscillation signal generatedby the source oscillator.

In addition, the local oscillation signal generation means may make alocal oscillation frequency of the local oscillation signal variable bysetting a dividing ratio variable by way of the setting means inaccordance with an arbitrary source oscillation frequency of the sourceoscillation signal generated by the source oscillator so that theintermediate frequency remains within a range regardless of the sourceoscillation frequency of the source oscillation signal.

Also, the signal generation means may make a frequency of the signalvariable by setting a dividing ratio variable by way of the settingmeans in accordance with an arbitrary source oscillation frequencygenerated by the source oscillator.

The demodulation apparatus according to the preferred embodiment of thepresent invention having the above construction shares sourceoscillators of at least the local oscillation signal generation meansand the signal generation means, thereby setting it variable by way ofthe setting means the dividing ratios of at least the local oscillationsignal generation means and the signal generation means in accordancewith an arbitrary source oscillation frequency so that the intermediatefrequency remains within a predetermined range regardless of the sourceoscillation frequencies of the source oscillator.

Therefore, according to the demodulation apparatus according to thepreferred embodiment of the present invention, source oscillators for atleast the local oscillation signal generation means and the signalgeneration means are shared and the dividing ratios of at least thelocal oscillation signal generation means and the signal generationmeans are set variable by way of the setting means in accordance withthe arbitrary source oscillation frequency so that the intermediatefrequency remains within a predetermined range regardless of the sourceoscillation frequencies of the source oscillation signal, therebyenabling the demodulation apparatus to support or cope with variousoscillation frequencies, to eliminate the need for making the necessarysource oscillation frequency a predetermined frequency, and to utilize astandard oscillator as the source oscillator.

Also, in order to alleviate the above mentioned problems, a receivingapparatus according to another preferred embodiment of the presentinvention has assembled therein a position measurement unit forcalculating the apparatus' own position and speed upon receiving asignal from a satellite, the apparatus including: a receiving means forreceiving the signal from the satellite; a frequency conversion meansfor converting frequencies of high frequency signals received by thereceiving means into intermediate frequencies; a signal processing meansfor performing a signal processing on an intermediate frequency signalhaving the intermediate frequency obtained through the frequencyconversion means; a setting means for performing settings on thefrequency conversion means and the signal processing means; and a sourceoscillator for generating an operation clock for another unit achievinga function that differs from the position measurement unit and forgenerating a source oscillation signal including a predetermined sourceoscillation signal; wherein the frequency conversion means includes alocal oscillation signal generation means for generating a localoscillation signal having a local oscillation frequency for converting afrequency of the high frequency signal into an intermediate frequencybased on a source oscillation signal generated by the source oscillator;and the signal processing means includes a signal generation means forsharing the local oscillation signal generator means and the sourceoscillator and generating a signal having a predetermined frequencybased on the source oscillation signal generated by the sourceoscillator.

The receiving apparatus according to the preferred embodiment of thepresent invention having the above construction shares at least thesource oscillators for the local oscillation signal generation means andthe signal generation means in the position measurement unit and alsoshares the source oscillator provided for generating the operation clockfor another unit for achieving a predetermined function different fromthe position measurement unit, thereby setting variable by way of thesetting means the dividing ratios of at least the local oscillationsignal generation means and the signal generation means in accordancewith arbitrary source oscillation frequency so that the intermediatefrequency remains within a predetermined range regardless of the sourceoscillation frequencies of the source oscillation signal.

Therefore, according to the receiving apparatus of to the preferredembodiment of the present invention, source oscillators for at least thelocal oscillation signal generation means and the signal generationmeans in the position measurement unit are shared and also the sourceoscillator provided for generating the operation clock in another unitfor achieving a predetermined function other than achieving the functionof the position measurement unit is shared, and the dividing ratios ofat least the local oscillation signal generation means and the signalgeneration means are set variable by way of the setting means inaccordance with arbitrary source oscillation frequency so that theintermediate frequency remains in a predetermined range regardless ofthe source oscillation frequencies of the source oscillation signal. Inthis manner, various oscillation frequencies may be supported and astandard oscillator can be utilized as the source oscillator because thenecessary source oscillation frequency not necessarily includes aparticular frequency. In addition, cost reduction and downsizing of thereceiving apparatus may be achieved upon utilizing as the sourceoscillation frequencies the oscillation frequencies of the oscillatoralready installed in electronic apparatus having a predeterminedfunction.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent to those skilled in the art from the followingdescription of the present exemplary preferred embodiments of thepresent invention taken in conjunction with the accompanying drawings,in which:

FIG. 1 is a block diagram for describing the construction of a portablephone device as an example of preferred embodiment of the presentinvention;

FIG. 2 is a block diagram for describing the construction of a digitalmatched filter utilizing FFT which can be applied to the synchronizationcapture portion of the portable phone device of FIG. 1;

FIG. 3 is a block diagram for describing an actually installed exampleof the digital matched filter of FIG. 2 as the synchronization captureportion of the portable phone device of FIG. 1;

FIG. 4 is a block diagram for describing the construction of thesynchronization hold portion of the portable phone device of FIG. 1;

FIG. 5 is a block diagram for describing the construction of the channelcircuit in the synchronization hold portion of the portable phone devicein FIG. 1;

FIG. 6 is a chart for describing phase synchronization of the spreadcode in the synchronization hold portion of the portable phone device ofFIG. 1.

FIG. 7 is a chart for describing the phase correction of the spread codein the synchronization hold portion of the portable phone device in FIG.1;

FIG. 8 is a block diagram for describing the construction of a frequencysynthesizer in the frequency converter portion of the portable phonedevice of FIG. 1;

FIG. 9 shows diagrams for describing the construction of a LPF, whereinFIG. 9A is the construction of a IIR filter, while FIG. 9B is theconstruction of a RC filter;

FIG. 10 shows diagrams for describing the construction of the equivalentcircuits of a complete integration type loop filter, wherein FIG. 10A isthe construction of the loop filter and FIG. 10B is the equivalentcircuit of the loop filter as shown in FIG. 10A;

FIG. 11 is a diagram for describing the construction of a completeintegration type loop filter;

FIG. 12 is a block diagram for describing the construction of a NCO in asynchronization hold portion of the portable phone device in FIG. 1;

FIG. 13 is timing chart for describing the sampling timing correction ofthe sampler in the synchronization capture portion of the portable phonedevice in FIG. 1;

FIG. 14 is a chart for describing the construction of a signal from aGPS satellite;

FIG. 15 is a graph for describing the frequency search as a conventionalsynchronization processing of spread code and carrier; and

FIG. 16 is a graph for describing an example of the output waveformindicating time variation of the correlation value that is detected byusing the digital matched filter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, specific examples of preferred embodiment to which the presentinvention is applied will be described in detail hereunder by referenceto the accompanying drawings.

This preferred embodiment of the present invention includes a portablephone device having a GPS receiving function installed therein, in whichsignals from at least four GPS satellites are received in order tocalculate a position of the portable phone device itself based on thereceiving signals by applying a global positioning system (referred toas GPS below) which is a kind of GNSS system (Global NavigationSatellites System) for measuring position of a moving object on thesurface of the Earth by utilizing artificial satellites. The portablephone device receives as a receiving signal a spectrum spread signalwave conventionally known as an L1 band, C/A (Clear and Acquisition)code from a GPS unit which is one of the constituent elements ofachieving the function of the GPS receiver. An oscillator for generatingthe clock for the GPS unit is shared with the oscillator for generatingthe clock necessary for the function of an ordinary telephone. Bychanging settings of various portions of the GPS unit in accordance withan arbitrary oscillation frequency of the oscillator, it is possible tosupport various oscillation frequencies, thereby achieving costreduction and downsizing.

It is to be noted that the GPS unit in the portable phone device asshown in FIG. 1 separates the function of capturing synchronizationbetween the spread code of the pseudo-random noise (PN) generated byitself for demodulating the receiving signal and the function forholding synchronization between the spread code and the carrier, therebyincreasing the synchronization capture speed with a small scale circuit.

As shown in FIG. 1, the portable phone device 10 includes a telephoneunit 11 which is a unit for achieving the function of an ordinarytelephone, a crystal oscillator (X'tal Oscillator which is referred toas XO below) 12 for generating an oscillation signal D1 having apredetermined frequency, a temperature controlled X'tal oscillator(referred to as TCXO below) 13 for generating an oscillation signal D2having a predetermined oscillation frequency Fosc which is differentfrom that of the XO 12 and a multiplier/divider 14 for multiplyingand/or dividing the oscillation signal D2 supplied from the TCXO 13.

The telephone unit 11 is, e.g., a unit collectively referring to varioussections for realizing the function of an ordinary telephone such asbase band processing of a receiving signal and audio conversionprocessing. The telephone unit 11 is operated by using a clock based onthe oscillation frequency of the oscillation signal D2 which is suppliedfrom the TCXO 13 as the operation clock.

The XO 12 generates an oscillation signal D1 having a predeterminedoscillation frequency, e.g., around 32.768 kHz. The XO 12 supplies thegenerated oscillation signal D1 to an RTC (Real Time Clock) 28 whichwill be described hereinafter.

The TCXO 13 is provided to be used primarily for the operation clock ofthe telephone unit 11 and generates the oscillation signal D2 having apredetermined oscillation frequency Fosc, e.g., around 16.384 MHz, whichis different from that of the XO 12. The TCXO 13 supplies the generatedoscillation signal D2 to the telephone unit 11, the multiplier/divider14 and a frequency synthesizer 19 which will be described hereinafter,and the like.

The multiplier/divider 14 multiplies by a predetermined multiplicationfactor or divides by a predetermined dividing ratio the oscillationsignal D2 supplied from the TCXO 13 based on a control signal D3supplied from a CPU (Central Processing Unit) 27 which will be describedhereinafter. The multiplier/divider 14 supplies a multiplied/dividedoscillation signal D4 to a synchronization capture portion 25 which willbe described hereinafter, a synchronization hold portion 26 which willbe described hereinafter, the CPU 27, a timer 29 which will be describedhereinafter and a memory 30 which will be described hereinafter.

The portable phone device 10 also includes an antenna 15 for receivingRF (Radio Frequency) signals transmitted from the GPS satellites, a lownoise amplifier (referred to as LNA below) 16 for amplifying the RFsignals D5 received by the antenna 15, a band pass filter (referred toas BPF below) 17 for passing particular frequency components in theamplified RF signal D6 amplified by the LNA 16, an amplifier 18 forfurther amplifying the amplified RF signal D6 as passed through the BPF17, the frequency synthesizer 19 for generating a local oscillationsignal D10 having a predetermined frequency Flo based on the oscillationsignal D2 supplied from the TCXO 13, a mixer 20 for multiplying theamplified RF signal D8 having a predetermined frequency Frf as amplifiedby the amplifier 18 by the local oscillation signal D10 supplied fromthe frequency synthesizer 19, a low pass filter (referred to as LPFbelow) 22 for passing predetermined frequency components of an amplifiedIF signal D12 which is amplified by the amplifier 21 and ananalog-to-digital converter (referred to as A/D below) 23 for convertingan analog form amplified IF signal D13 passed through the LPF 22 into adigital form amplified signal D14.

The antenna 15 receives the spread carrier RF signals having a frequencyof 1575.42 MHz which are transmitted from the GPS satellites. The RFsignals D5 received by the antenna 15 are supplied to the LNA 16.

The LNA 16 amplifies the received RF signals D5 which are received bythe antenna 15. The LNA 16 supplies the amplified RF signal D6 to theBPF 17.

The BPF 17 includes a so-called SAW (Surface Acoustic Wave) filter andpasses predetermined frequency components of the amplified RF signal D6which is amplified by the LNA 16. The amplified RF signal D7 passedthrough the BPF 17 is supplied to the amplifier 18.

The amplifier 18 further amplifies the amplified RF signal D7 passedthrough the BPF 17. The amplifier 18 supplies the amplified RF signal D8having a predetermined frequency Frf, in other words., 1575.42 MHz tothe mixer 20.

The frequency synthesizer 19 generates the local oscillation signal D10having a predetermined frequency Flo based on the oscillation signal D2supplied from the TCXO 13 under control of the control signal D9supplied from the CPU 27. At this event, as details will be describedhereinafter, the frequency synthesizer 19 changes the setting inaccordance with the oscillation frequency Fosc of the oscillation signalD2 generated by the TCXO 13. The frequency synthesizer 19 supplies thegenerated local oscillation signal D10 to the mixer 20.

The mixer 20 down converts the amplified RF signal D8 by multiplying theamplified RF signal D8 having the predetermined frequency Frf andamplified by the amplifier 18 by the local oscillation signal D10supplied from the frequency synthesizer 19, thereby producing the IFsignal D11 having the predetermined frequency Fif, e.g., 1.023 MHz. TheIF signal D11 produced by the mixer 20 is supplied to the amplifier 21.

The amplifier 21 amplifies the IF signal D11 which is down converted bythe mixer 20. The amplifier 21 supplies the amplified IF signal D12 tothe LPF 22.

The LPF 22 allows frequency components to pass, which are lower than thepredetermined frequency within the amplified IF signal D12 which isamplified by the amplifier 21. It is to be noted that the LPF 22 canchange its characteristics such as the pass band frequency width and thelike, if necessary, in accordance with the oscillation frequency Fosc ofthe oscillation signal D2 generated by the TCXO 13 which will bedescribed in detail hereinafter. The amplified IF signal D13 passedthrough the LPF 22 is supplied to the A/D 23.

The A/D 23 converts the analog form amplified IF signal D13 passedthrough the LPF 22 into the digital form amplified IF signal D14. Theamplified IF signal D14 which is converted into the digital form by theA/D 23 is supplied to both of the synchronization capture portion 25 andthe synchronization hold portion 26.

It is to be noted that, among various portions in the portable phonedevice 10, those portions including the LNA 16, the BPF 17, theamplifiers 18, 21, the frequency synthesizer 19, the mixer 20, the LPF22 and the A/D 23 constitute a frequency conversion portion 24 for downconverting the received RF signal D5 having a higher frequency 1575.42MHz as received by the antenna 15 into the amplified IF signal D14having a lower frequency, e.g., about 1.023 MHz for ease of digitalsignal processing.

Moreover, the portable phone device 10 includes the synchronizationcapture portion 25 for capturing synchronization of the spread codegenerated by itself and the spread code in the amplified IF signal D14supplied from the A/D 23 and also detecting the carrier frequency in theamplified IF signal D14, the synchronization hold portion 26 for holdingsynchronization between the spread code in the amplified IF signal D14supplied from the A/D 23 and the carrier as well as for demodulatingmessages, a CPU 27 for performing various processing by integrallycontrolling the entire portions, an RTC 28 for measuring time based onthe oscillation signal D1 supplied from the XO 12, a timer 29 acting asthe internal timer for the CPU 27 and a memory 30 including a RAM(Random Access Memory), a ROM (Read Only Memory) and the like.

The synchronization capture portion 25 performs coarse synchronizationcapturing of the spread code in the amplified IF signal D14 suppliedfrom the A/D 23 based on the multiplied/divided oscillation signal D4supplied from the multiplier/divider 14 under control of the CPU 27.Also performed by the synchronization capture portion 25 is the carrierfrequency detection of the amplified IF signal D14. At this event, aswill be described in detail hereinafter, the synchronization captureportion 25 changes the settings in accordance with the oscillationfrequency Fosc of the oscillation signal D2 generated by the TCXO 13.The synchronization capture portion 25 supplies the detected satellitenumber for identifying each GPS satellite, the phase of the spread codeand the carrier frequency to the synchronization hold portion 26 and theCPU 27.

Under control of the CPU 27, the synchronization hold portion 26performs synchronization holding between the spread code in theamplified IF signal D14 supplied to the A/D 23 and the carrier based onthe multiplied/divided oscillation signal D4 supplied from themultiplier/divider 14. The synchronization hold portion 26 alsodemodulates the navigation message included in the amplified IF signalD14. At this event, as the details will be described hereinafter, thesynchronization hold portion 26 makes the settings variables inaccordance with the oscillation frequency Fosc of the oscillation signalD2 generated by the TCXO 13. Also, the synchronization hold portion 26starts operation with the initial values of the satellite number, thephase of the spread code and the carrier frequency supplied from thesynchronization capture portion 25. The synchronization hold portion 26holds synchronization of the amplified IF signals D14 from a pluralityof GPS satellites in a parallel manner and supplies phases, carrierfrequencies and navigation messages of the detected spread codes to theCPU 27.

The CPU 27 performs various processing such as acquiring phases, carrierfrequencies and navigation messages of the spread codes supplied fromthe synchronization hold portion 26 for calculating the position and thespeed of the portable phone device 10 based on the various informationas well as correcting time information of the portable phone device 10based on the accurate time information of the GPS satellites which areobtained from the navigation messages. Also, the CPU 27 integrallycontrols various portions, various peripherals and input/output devicesof the portable phone device 10.

The RTC 28 measures time based on the oscillation signal D1 suppliedfrom the XO 12. The time information which is measured by the RTC 28 isused as a replacement until the accurate time information of the GPSsatellite is acquired and is suitably corrected by controlling the XO 12under control of the CPU 27 when it acquires the accurate timeinformation of the GPS satellites.

The timer 29 has a function as an internal clock for the CPU 27 and isused for generating various timing signals and the time referencenecessary for proper operation of various portions. For example, in theportable phone device 10, the timer 29 is referred to by thesynchronization hold portion 26 after phase synchronization with thespread code synchronization captured by the synchronization captureportion 25 as the timing for initiating operation of a spread codegenerator which will be described hereinafter.

The memory 30 includes a RAM, a ROM and the like. In the memory 30, theRAM is used as a working area for various processing by the CPU 27 andthe like. The RAM is also used in case of buffering various input dataas well as for saving intermediate data in the process of operations anddata for final results of operations. Also, in the memory 30, the ROM isused as means of storing various programs, fixed data and the like.

It is to be noted that the synchronization capture portion 25, thesynchronization hold portion 26, the CPU 27, the RTC 29 and the memory30 in the portable phone device 10 constitute a base band processingportion.

In the portable phone device 10 including the above mentioned variousportions, it is possible to fabricate the entire portions at leastexcluding the XO 12, the TCXO 13, the antenna 15, the LNA 16 and the BPF17 as an integrated single chip demodulation circuit 31.

The portable phone device 10 not only achieves the function of anordinary telephone but also receives RF signals from at least four GPSsatellites in case of functioning as the GPS receiver using the GPSunit. The received RF signals are converted into the IF signal by thefrequency conversion portion 24 for synchronization capturing of thespread code and the carrier frequency detection by the synchronizationcapture portion 25. The synchronization hold portion 26 performssynchronization capturing of the spread code and demodulates thenavigation messages. And then, the portable phone device 10 calculatesthe position and speed of the own portable phone device 10 by the CPU 27based on the phase of the spread code, the carrier frequency and thenavigation messages.

Now, the synchronization capture portion 25 and the synchronization holdportion 26 in the portable phone device 10 will be described. Asdescribed above, it is to be noted that the present example of preferredembodiment of the present invention features in separate thesynchronization capture function and the synchronization hold functioninto the synchronization capture portion 25 and the synchronization holdportion 26, respectively. Also, a description will be given herein aboutthe reasons for separating such functions.

As described hereinabove, the synchronization capture portion 25performs the synchronization capturing of the spread code in the IFsignal and the carrier frequency detection, at high speed. In order toperform the synchronization capturing of the spread code at a highspeed, the synchronization capture portion 25 utilizes a matched filter.Specifically, the synchronization capture portion 25 may use, e.g., adigital matched filter 50 utilizing FFT as the matched filter as shownin FIG. 2.

Specifically, as shown in FIG. 2, input to the digital matched filter 50is the IF signal from the frequency conversion portion 24 of the signalcorresponding to the amplified IF signal D14 which is received by theantenna 15 and then sampled by a sampler 51 for sampling the If signalat the sampling frequency based on the oscillation signal D2 generatedby the TCXO 13. The digital matched filter 50 includes a memory 52 forbuffering the IF signal sampled by the sampler 51, an FFT processingportion 53 for performing FFT processing by reading out the IF signalbuffered in the memory 52, a memory 54 for buffering the frequencydomain signal FFT processed by the FFT processing portion 53, a spreadcode generator 55 for generating the same spread code as the spread codein the RF signals from the GPS satellites, an FFT processing portion 56for FFT processing the spread signal generated by the spread codegenerator 55, a memory 57 for buffering the frequency domain signal FFTprocessed by the FFT processing portion 56, a multiplier 58 formultiplying common complex of either one of the frequency domain signalsbuffered in the memories 54 and 57 by the other, an inversed fastFourier transformation (referred to as IFFT below) processing portion 59for performing IFFT of the frequency domain signal multiplied by themultiplier 58 and a peak detector 60 for detecting peak of correlationof the spread code in the RF signals from the GPS satellites based onthe correlation function as obtained by the IFFT processing of the IFFTprocessing portion 59 and the spread code generated by the spread codegenerator 55.

Such digital matched filter 50 is actually installed as software forimplementing each of the FFT processing portion 53, the spread codegenerator 55, the multiplier 58, the IFFT processing portion 59 and thepeak detector 60 by a DSP (Digital Signal Processor). In other words,the synchronization capture portion 25 to which the digital matchedfilter 50 is applied includes, e.g., as shown in FIG. 3, a sampler 71corresponding to the above-mentioned sampler 51, a RAM 72 correspondingto the above-mentioned memory 52, a RAM/ROM 73 including the programarea and the work area of the above-mentioned memories 54, 57 and theDSP and a DSP 74 for performing the processing of the above-mentionedFFT processing portions 53, 56, the spread code generator 55, themultiplier 58, the IFFT processing portion 59 and the peak detector 60.

The synchronization capture portion 25 performs sampling, e.g., an IFsignal of 1.023 MHz by the sampler 71 at 4.096 MHz and performs anoperation equivalent to the digital matched filter 50 by the DSP 74,thereby performing synchronization capturing of the spread code, i.e.,phase detection of the spread code in the IF signal with ¼ chipaccuracy. If the capacity of the RAM 72 is for 16 milliseconds, thesynchronization capture portion 25 performs the frequency domainoperation by the DSP 74 to detect the carrier in the IF signal (referredto as IF carrier below) frequency with the accuracy of 1/16 kHz (± 1/32kHz). Since the IF signals stored in the RAM 72 include signals from aplurality of GPS satellites, the synchronization capture portion 25 maydetect a plurality of GPS satellites by calculating the correlationamong the spread codes of a plurality of GPS satellites.

The portable phone device 10 can calculate the position and the speed ofthe portable phone device 10 based on the phases and the carrierfrequencies of the spread codes of at least four GPS satellites detectedby the synchronization capture portion 25.

However, in the portable phone device 10, the above-mentioned accuracyof ¼ chip for phase detection of the spread code and 1/16 kHz for thecarrier frequency detection is not enough for obtaining the desiredposition and speed calculation results of the portable phone device 10.In order to improve accuracy in the portable phone device 10, it isnecessary to take measures such as increasing the sampling frequency ofthe sampler 71 and increasing the time duration for storing the IFsignal. Such measures are assumed to accompany with increased memorycapacity of the memories such as the RAM and the like as well asextending the processing time for detecting the phase and carrierfrequency of the spread code. In addition, if the synchronizationcapture portion 25 does not receive the navigation message from externalmeans, the portable phone device 10 is required to demodulate thenavigation messages from at least four GPS satellites at every 20milliseconds. As a result, the DSP 74 has always to detectsynchronization and demodulate the navigation messages at a very highspeed, thereby resulting in increased cost due to larger hardware sizeand power consumption.

In view of such problem, in the portable phone device 10,synchronization capture is made in course accuracy by thesynchronization capture portion 25 and synchronization holding anddemodulation of the navigation messages of a plurality of GPS satellitesare made by the synchronization hold portion 26.

The synchronization capture portion 25 supplies the satellite numbers,the phases and carrier frequencies of the detected GPS satellites to thesynchronization hold portion 26. On the other hand, the synchronizationhold portion 26 starts operating with various information received fromthe synchronization capture portion 25 as the initial values. Thesynchronization hold portion 26 adjusts the start timing of the spreadcode which is generated by a DLL (Delay Locked Loop) to be describedhereinafter based on the phase of the spread code. It is to be notedthat the portable phone device 10 sets the spread code to be generatedin accordance with the satellite number of the detected GPS satellite.At this event, the portable phone device 10 is affected by errors of theDoppler shift and the oscillation frequency of the oscillation signalgenerated by oscillators such as the TCXO 13 and the like. However,since the spread code is basically repeated at every 1 millisecondinterval, the start timing of the spread code to be generated by the DLLcircuit may be shifted to multiples of 1 millisecond.

It is to be noted that since the carrier frequency includes errors ofthe TCXO 13 which generates the sampling clock for acquisition of the IFsignal into memories such as the above-mentioned RAM and the like, evenif the above mentioned resolution problem is solved, it is not theaccurate value, or the sum of the carrier frequency and the Dopplershift. However, in the portable phone device 10, if the synchronizationcapture portion 25 and the synchronization hold portion 26 are operatingon the same oscillator, i.e., the clock originated by the TCXO 13, theboth include the same frequency error, thereby causing no problem forthe synchronization hold portion 26 to start operation with the IFcarrier frequency detected by the synchronization capture portion 25 asthe initial value.

In order to perform synchronization holding of a plurality of GPSsatellites in a parallel manner, the synchronization hold portion 26 isprovided with, e.g., a plurality of independent channel circuits 81 ₁,81 ₂, . . . , 81 _(N) as shown in FIG. 4. These channel circuit 81 ₁, 81₂, . . . , 81 _(N) are assigned to respective detection results of thesynchronization capture portion 25 under the setting of a controlregister 82.

As shown in FIG. 5, the channel circuits 81 ₁ to 81 _(N) are constructedbasically the same as a combination of an IF carrier synchronizationCostas loop 101 and a spread code synchronization DLL 102 for achievingboth of the synchronization capturing and the synchronization holding inthe conventional GPS receiver.

Specifically, as shown in FIG. 5, input to the Costas loop 101 in thechannel circuits 81 ₁, 81 ₂, . . . , 81 _(N) is a signal multiplied by amultiplier 103 for multiplying an IF signal corresponding to theamplified IF signal D14 obtained by the above-mentioned antenna 15 andthe frequency conversion portion 24 by the spread code generated by aspread code generator (PN generator which is referred to as PNG below)128 which will be described hereinafter and having the phase P (Prompt).On the other hand, in the DLL 102 in the channel circuits 81 ₁, 81 ₂, .. . , 81 _(N) there is input an IF signal corresponding to the amplifiedIF signal D14 of the above-mentioned antenna 15 and the frequencyconversion portion 24.

In the Costas loop 101, a multiplier 105 multiplies the input signal bya sine component (in-phase component) of a reproduced carrier generatedby an NCO (Numeric Controlled Oscillator) 104, while a multiplier 106multiplies the input signal by a cosine component (quadrature component)of the reproduced carrier generated by the NCO 104. In the Costas loop101, predetermined frequency components of the in-phase componentssignal from the multiplier 105 are allowed to pass through an LPF 107before being supplied to a phase detector 110, a digitizing circuit 111and a squared sum circuit 112. On the other hand, predeterminedfrequency components of the quadrature components signal from themultiplier 106 in the Costas loop 101 are allowed to pass through an LPF108 before being supplied to the phase detector 110 and the squared sumcircuit 112. The phase detector 110 in the Costas loop 101 detects phaseinformation based on the output signals from the LPF 107, 108 and thedetected phase information is supplied to the NCO 104 through a loopfilter 109. Also, in the Costas loop 101, the output signals from theLPF 107, 108 are supplied to the squared sum circuit 112 whichcalculates the squared sum (I²+Q²) for outputting the correlation value(P) of the spread code having the phase P. Furthermore, in the Costasloop 101, the output signal from the LPF 107 is supplied to thedigitizing circuit 101 to provide the digitized information as thenavigation message.

On the other hand, in the DLL 102, a multiplier 113 multiplies the inputIF signal by the spread code E (Early), which is early in phase ascompared to the phase P generated by an PNG 128. Also, a multiplier 114multiplies the input IF signal by the spread code L (Late) lagged inphase as compared to the phase P generated by the PNG 128. In the DLL102, a multiplier 115 multiplies the signal from the multiplier 113 bythe sine component of the reproduced carrier generated by the NCO 104 inthe Costas loop 101 and a multiplier 116 multiplies the signal from themultiplier 113 by the cosine component of the reproduced carriergenerated by the NCO 104. In the DLL 102, predetermined frequencycomponents among the in-phase components signal produced by themultiplier 115 are allowed to pass through an LPF 117 before beingsupplied to a square sum calculation circuit 119. On the other hand, inthe DLL 102, predetermined frequency components signal among thequadrature components signal are allowed to pass through an LPF 118before being supplied to the square sum calculation circuit 119. Inaddition, in the DLL 102, a multiplier 120 multiplies the signaloutputted from the multiplier 114 by the signal components among thereproduced carrier generated by the NCO 104 in the Costas loop 101.Similarly, a multiplier 121 multiplies the signal outputted from themultiplier 114 by the cosine components signal of the reproduced carriergenerated by the NCO 104. In the DLL 102, predetermined frequencycomponents of the in-phase components signal outputted from themultiplier 120 are allowed to pass through an LPF 122 before beingsupplied to a squared sum calculation circuit 124. On the other hand, inthe DLL 102, predetermined frequency components of the quadraturecomponents signal outputted from the multiplier 121 are allowed to passthrough an LPF 123 before being supplied to the squared sum calculationcircuit 124.

In the DLL 102, signals outputted from the squared sum calculationcircuits 119, 124 are supplied to a phase detector 125 and phaseinformation detected by the phase detector 125 based on these signals issupplied to an NCO 127 through a loop filter 126 before being suppliedto an NCO 127. Moreover, the above-mentioned spread codes having thephases E, P and L are generated by the PNG 128 based on the signalhaving the predetermined frequency generated by the NCO 127.Furthermore, in the DLL 102, the squared sum (I²+Q²) calculated throughthe squared sum calculation circuit 119 is outputted as a correlationvalue (E) of the spread code having the phase E, while the squared sum(I²+Q²) calculated through the squared sum calculation circuit 124 isoutputted as a correlation value (L) of the spread code having the phaseL.

As described hereinabove, in the synchronization hold portion 26 havingchannel circuits 81 ₁, 81 ₂, . . . , 81 _(N) as constructed in a similarmanner as a combination of the IF carrier synchronization Costas loop101 and the spread code synchronization DLL 102, the satellite number ofthe GPS satellite, the phase of the spread code and the carrierfrequency are set as the initial values before start operating. Suchsetting of the initial values may be made by directly communicating withthe synchronization capture portion 25 or by way of the CPU 27 forcontrolling the synchronization capture portion 25 and thesynchronization hold portion 26.

Such synchronization hold portion 26 is synchronized with the spreadcode in the following manner. As shown in FIG. 6, the timer is made tostart at the timing of acquisition of the IF signal into a memory suchas the RAM 72 and the like by the synchronization capture portion 25.When the synchronization capture portion 25 detects the phase h of thespread code for the IF signal stored in the memory, the synchronizationhold portion 26 synchronizes in phase with the spread code of thereceived signal by starting the spread code which is generated by theDLL 102 at the time shifted equal to the h after receipt of the phase hand multiple times of 1 millisecond of the same timer. It is to be notedthat in FIG. 6, “PN” indicates a PN series code, i.e., the spread code.

On the other hand, since the phase of the spread code in the receivingsignal is unknown in the conventional circuit combining the Costas loopand the DLL, the IF carrier frequency generated by the DLL and theperiod of the spread code are shifted by a small amount, therebydetecting the phase having a meaningful strong correlation in the courseof sliding the phase of the IF signal with respect to the spread code.As a result, it took a considerably long time before establishingsynchronization in the conventional circuit, because, in the worst caseof detecting the phase, it is required to detect all phases of thecarrier frequency in the range of several kHz and the spread code havingthe 1023 code length.

On the contrary, in the portable phone device 10 in which thesynchronization hold portion 26 has basically the same construction asthe conventional circuit, since the initial values of the phase of thespread code that the synchronization hold portion 26 receives and the IFcarrier frequency are different from the correct values by a smallamount, the phase having a meaningful strong correlation is always inexistence near the initial value even if any error may be included. As aresult, similar to the conventional circuit, the synchronization holdportion 26 conducts search for the meaningful strong correlation bychanging the signals generated from the NCOs 104, 127 near their initialvalues while stopping the control of the loop filters 109, 126 in theCostas loop 101 and the DLL 102. After detection of the correlation, itis switched to the controls by the loop filters 109, 126, respectively.In the above manner, the synchronization hold portion 26 can establishphase synchronization of the spread code by the DLL 102 and phasesynchronization of the carrier by the Costas loop 101 in a short time.Such synchronization may be maintained thereafter. Since the initialvalue of the frequency of the reproduced carrier generated by the NCO104 may be set within the error range of tens of Hz with respect to theIF carrier frequency in the synchronization hold portion 26, narrowbandwidths of the LPFs 107, 108, 118, 122 and 123 and the loop filters109 and 126 may be set from the beginning, thereby establishingsynchronization in a condition of high S/N (Signal to Noise ratio).

In the portable phone device 10, if the synchronization hold portion 26can be operated on the clock of, e.g., 1.023×16=16.368 MHz and the phaseof the spread code is detected with a time resolution of 1/16.368 MHz inthe DLL 102, it is possible to calculate the pseudo-distance to the GPSsatellite with the 1/16 chip accuracy based on the phase of the spreadcode. Also, if it is constructed to control the NCO 104 in the Costasloop 101 by the unit of 1 Hz, the resolution of the IF carrier frequencyis 1 Hz and synchronization may be maintained in such accuracy by theDLL 102 and the Costas loop 101.

As described hereinabove, in the portable phone device 10, if oncesynchronization is held by the synchronization hold portion 26, it ispossible to continuously calculate and output the position of theportable phone device 10 based on the phase of the spread code generatedby the DLL 102. It is also possible to continuously calculated andoutput the speed of the portable phone device 10 based on the IF carrierfrequency obtained by the Costas loop 101.

Also as described hereinabove, the synchronization hold portion 26 usesthe phase of the spread code and the IF carrier frequency received fromthe synchronization capture portion 25 as the initial values, therebyconducting search for any meaningful strong correlation near theseinitial values. One of the reasons is that the oscillator or TCXO 13 asthe clock source installed in the portable phone device 10 includes anerror with respect to its nominal frequency. In the portable phonedevice 10, if the synchronization capture portion 25 is constructed byusing the digital matched filter 50 utilizing FFT as shown in FIG. 2,since the IF signal is first stored in the memory and then the detectionresult of the synchronization hold portion 26 is supplied after theprocessing time of the DSP, there causes an error of T×ΔFosc/Fosc at thetime of supplying the detection result to the synchronization holdportion 26, where ΔFosc is the error from the nominal frequency of theoscillator and T (seconds) is the processing time of the DSP. Forexample, if T=3 seconds and ΔFosc/Fosc is within ±3 ppm in the portablephone device 10, there is an error of ±9 microseconds=withinapproximately ±9 chips. This means that, in the portable phone device10, an error becomes larger if the DSP processing takes longer time.

In addition, in the portable phone device 10, a Doppler shift of thecarrier frequency caused by the relative movement between the GPSsatellites and the portable phone device 10 is another factor that maycause errors. In the portable phone device 10, if the carrier frequencyFrf=1575.42 MHz and the Doppler shift of the receiving signal is ΔFd,the period of the spread code is approximately (1−ΔFd/Frf) times of 1millisecond, caused by the Doppler shift. For example, in case of +5 to−5 kHz range of Doppler shift, there causes an error of approximately−9.5 to 9.5 microseconds=approximately −9.5 to 9.5 chips in 3 seconds.

These two examples are relatively close to the actual case. In theportable phone device 10, if the both errors of the oscillator anderrors caused by the Doppler shift are combined, the total error may bein the range of approximately ±20 chips. This means that the correlationmay be detected by conducting the search only within this range. Forexample, the synchronization hold portion 26 starts generating thespread code to be generated by the DLL 102 earlier than the phase of thespread code supplied from the synchronization capture portion 25 by 20chips and the frequency setting of the NCOs 104, 127 as the period ofthe spread code at that time can be set to longer than (1+5/1575.420)milliseconds. In this way, slide of the spread code of the signal fromthe GPS satellite included in the IF signal can be started at the timeshifted by +20 chips, thereby conducting a search for the correlationwhile the spread codes are mutually shifting for a suitable timeinterval.

As described hereinabove, although correlation detection is carried outby changing the range of 1023 chips and in the range of the IF carrierfrequency equal to the error of the oscillator and the Doppler shift inthe conventional circuit using the DLL and the Costas loop, there isonly a minor error in the initial value of the carrier frequency in theportable phone device 10. As a result, the range of detection of thecorrelation may be only a few tenths, thereby significantly shorteningthe time required for establishing synchronization in thesynchronization hold portion 26.

As apparent from the above description, the portable phone device 10features in separate the synchronization capturing function and thesynchronization holding function, thereby enabling the synchronizationcapture portion 25 to promptly detect the phases of the spread codes andthe IF carrier frequencies of the signals from the GPS satellites whichare included in the IF signal. The synchronization holding portion 26can promptly shift to a synchronization holding operation based on suchdetection results. However, in the portable phone device 10, theprocessing time of the synchronization capture portion 25 becomes longerin cases where the processing sequence increases for detecting weaksignals from GPS satellites included in the IF signal, thesynchronization capture portion 25 is operated on a slower clock inorder to suppress power consumption and the like. This is accompaniedwith wider range of searching for establishing synchronization in thesynchronization hold portion 26, thus not desirable.

In general, in the GPS receiver, a common crystal oscillator is used asa local oscillator in the frequency conversion portion and the sourceoscillator in order to generate the clock for signal processing in thebase band processing portion. Similarly, in the portable phone device 10as shown in FIG. 1, the TCXO 13 is shared as the source oscillator ofthe local oscillator in the frequency conversion portion 24 and thesource oscillator for the operation clock in the synchronization captureportion 25 and the synchronization hold portion 26. And thesynchronization hold portion 26 corrects the phase h of the spread codeto h+Δh (Δh=−T×ΔFif/Frf) as shown in FIG. 7, where ΔFif is thedifference between the IF carrier frequency detected by thesynchronization capture portion 25 and the IF frequency Fif, e.g., 1.023MHz based on the nominal value of the TCXO 13, Frf is the carrierfrequency of 1575.42 MHz of the signal from the GPS satellite, T(seconds) is the time required for synchronization capturing from thetime of acquisition of IF signal into the memory by the synchronizationcapture portion 25 and h is the phase of the spread code. For example,if ΔFif=+3 kHz and T=10 seconds, Δh=−19 microseconds=approximately −19chips. By making such corrections, the synchronization hold portion 26can accurately correct phase difference of the spread code caused by theerror in the oscillation frequency Fosc of the TCXO 13 and the Dopplershift, thereby establishing synchronization by searching in the range ofabout 1 chip even if it may take tens of milliseconds for thesynchronization capture operation in the synchronization capture portion25.

The reason why such correction is possible will be described hereunder.

In the portable phone device 10, in order to convert the known carrierfrequency Frf of the signal from the GPS satellite in the frequencyconversion portion 24 into a known intermediate frequency Fif, thefrequency synthesizer 19 generates the local oscillation frequencyFlo=N×Fosc (N is a constant sufficiently smaller than 1) based on theTCXO 13 of the nominal oscillation frequency, thereby providingFif=Frf−Flo. It is to be noted that the signal actually received fromthe GPS receiver is the addition of the intermediate frequency Fif andthe error ΔFif due to errors in the oscillation frequency Fosc of theTCXO 13 and the Doppler shift. Namely, in the portable phone device 10,Fif+ΔFif=Frf+ΔFd−Flo=Frf+ΔFd−N×(Fosc+ΔFosc), where ΔFd is the amount ofDoppler shift and ΔTosc is the error from the nominal oscillationfrequency of the TCXO 13. As a result, in the portable phone device 10,the IF carrier frequency detected by the synchronization capture portion25 is Fif+ΔFif, ΔFif=ΔFd−N×ΔFosc. It is important to note that, what canbe detected by the synchronization capture portion 25 is only ΔFif. ΔFdand ΔFosc are unknown at an initial synchronization capturing stage.

Assuming that the timer counts 1 millisecond which is one period of thespread code by the nominal oscillation frequency of the TCXO 13, theactual time will be 1 millisecond×Fosc/(Fosc+ΔFosc)≈(1−ΔFosc/Fosc) dueto the error ΔFosc. On the other hand, due to the Doppler shift ΔFd, thelength of 1 period of the spread code in the receiving signal is 1millisecond×Fosc/(Fosc+ΔFd)≈(1−ΔFsoc/Frf). As a result, the ratio of thelength of 1 period of the spread signal in the receiving signal and the1 millisecond as counted by the nominal oscillation frequency of theTCXO 13 is given by:(1−ΔFd/Frf)/(1−ΔFosc/Fosc)≈1−ΔFd/Frf+ΔFosc/FoscThe right side in the above expression can modified as follows:1−ΔFif/Frf+(ΔFosc/Fosc)×(Fif/(N×Fosc))≈1−ΔFif/FrfAs apparent from the above, in the portable phone device 10, it can bewell approximated by the synchronization capture portion 25 in the formexcluding such unknown parameters as ΔFd and ΔFosc.

As understood from the above description, in the portable phone device10, the synchronization capture portion 25 performs the synchronizationcapture processing at the time of acquisition of IF signal. In a casewhen it took the time of T seconds until the time of supplying the phaseh of the detected spread code to the synchronization hold portion 26,there is a phase shift of −T×ΔFif/Frf from the phase of the detectedspread code which is detected by the synchronization capture portion 25.Consequently, as shown in FIG. 7, the synchronization hold portion 26may correct the phase shift of the spread code occurred in thesynchronization capture processing time by adding the correction valueΔh=−T×ΔFif/Frf to the phase h of the spread code supplied from thesynchronization capture portion 25, i.e., h+Δh in order to align thestart timing of the spread code which is generated by the DLL 102. Inthis manner, it is possible to detect the correlation in the range ofapproximately 1 chip, thereby establishing synchronization in a veryshort time. In the portable phone device 10, the correction value iscalculated through, e.g., CPU 27 and the synchronization captureprocessing by the synchronization capture portion 25 can be initiatedafter making phase correction by the synchronization hold portion 26.

Information necessary in making such phase correction of the spread codeis only the IF carrier frequency which is detected by thesynchronization capture portion 25. This means that such information asthe error in the oscillation frequency Fosc of the TCXO 13 and theDoppler shift value are unnecessary. In addition, in the portable phonedevice 10, there is no dependency to the IF carrier frequency and it isenough to modify only the sign of the ΔFif even if the local oscillationfrequency Flo is set so that Fif=Fro−Flo.

Now, as described hereinabove, the portable phone device 10 isconstructed in such a manner that the TCXO 13 provided primarily forgenerating the operation clock of the telephone unit 11 is also used bythe GPS unit. The TCXO 13 changes the oscillation frequency Fosc over alarge variety of ranges depending on types and the like of the portablephone device 10. As a result, the portable phone device 10 changes thesettings of various parts in the frequency conversion portion 24 and thebase band processing portion in order to correspond to variousoscillation frequencies Fosc.

Specifically, the portable phone device 10 is designed to make itvariable at least the local oscillation frequency Flo which is thefrequency of the local oscillation signal D10 generated by the frequencysynthesizer 19 in the frequency conversion portion 24 so that thefrequency, i.e., the intermediate frequency Fif of the amplified IFsignal D14 generated by the frequency conversion portion 24 remainswithin a predetermined range regardless of the oscillation frequencyFosc of the oscillation signal D2 which is generated by the TCXO 13.Also, the portable phone device 10 is designed to make it variable thefrequency settings of the above described Costas loop 101 and the NCOs104, 127 of the DLL 102 for demodulating the spread spectrum signalprovided as the synchronization hold portion 26 in the base bandprocessing.

Moreover, in the portable phone device 10, characteristics such as thepass band frequency of the LPF 22 in the frequency conversion portion 24is made variable if necessary. Furthermore, the portable phone device 10is designed to make it variable the frequency range of the NCO whichwill be described hereinafter and used for sampling clock for theabove-mentioned sampler 71 for sampling the amplified IF signal D14 inthe synchronization capture portion 25 at a predetermined samplingfrequency, the pass band frequencys of the Costas loop 101 and theabove-mentioned LPFs 107, 108, 117, 118, 122 and 123 of the DLL 102and/or the characteristics of the above-mentioned loop filters 109, 126.Details of these elements will be described hereunder.

Firstly, description will be made on a basic technique of making itvariable the settings in the frequency conversion portion 24.

In the portable phone device 10, the dividing ratio of the divider inthe frequency synthesizer 19 is made variable for generating the IFsignal D11 having the frequency Fif by down converting the amplified RFsignal D8 having the frequency Frf, thereby making it variable the localoscillation frequency Flo, i.e., the frequency of the local oscillationsignal D10.

Specifically, the frequency synthesizer 19 includes, e.g., as shown inFIG. 8, a PLL (Phase Locked Loop) synthesizer having variable dividingratios by four settings K1, K2, K3 and K4 which are controlled by theCPU 27. In other words, the frequency synthesizer 19 includes a divider131 for dividing the oscillation signal D2 supplied from the TCXO 13 bya predetermined dividing ratio, a phase comparator 132 for comparing thephases of the divided oscillation signal from the divider 131 and thesignal supplied from the down converter 136 which will be describedhereinafter, an LPF 133 for passing predetermined frequency componentsof the comparison signal from the phase comparator 132, a voltagecontrolled oscillator (referred to as VCO below) 134 which is anoscillator for providing an oscillation signal having a predeterminedfrequency based on the comparison signal passed through the LPF 133, apulse swallow counter 135 for dividing the oscillation signal suppliedfrom the VCO 134 by two predetermined dividing ratios which aredifferent by “1” under external control, the down counter 136 forcounting down the divided signal supplied from the pulse swallow counter135, a down counter 137 for down counting the signal supplied from anAND gate 140 which will be described hereinafter and a recording device138 such as a register, a memory and the like for holding the settingsK1, K2, K3, K4 set by the CPU 27. The construction of the frequencysynthesizer 19 is conventional and in general used.

The divider 131 divides the oscillation signal D2 supplied from the TCXO13 by the dividing ratio 1/K1 which is represented by the setting K1 setin the recording device 138 by the CPU 27. The divider 131 supplies thedivided oscillation signal to the phase comparator 132. And the dividedoscillation signal acts as a reference clock frequency for the PLL.

The phase comparator 132 compares the phases of the divided oscillationsignal supplied from the divider 131 and the signal supplied from thedown counter 136. The phase comparator 132 supplies a comparison resultsignal representing the result of the comparison to the LPF 133.

The LPF 133 acts as a loop filter for the PLL and passes only lowfrequency components lower than a predetermined frequency of thecomparison result signal supplied from the phase comparator 132. Thecomparison result signal passed through the LPF 133 is supplied to theVCO 134.

The VCO 134 generates an oscillation signal having a predeterminedfrequency based on the comparison result signal supplied from the LPF133, wherein the oscillation frequency of the VCO 134 varies based onthe voltage of the comparison result signal. The VCO 134 not onlysupplies the generated oscillation signal to the pulse swallow counter135 but also outputs the local oscillation signal D10 having theabove-mentioned local oscillation frequency Flo.

The pulse swallow counter 135 divides the oscillation signal from theVCO 134 by the dividing ratio of either 1/K2 or 1/(K2+1) represented bythe setting K2 set by the recording device 138 under control of the CPU27. The dividing ratio of the pulse swallow counter 135 is 1/K2 when thebinary signal supplied from the down counter 137 is “1” or 1/(K2+1) whenthe binary signal is “0”. The pulse swallow counter 135 supplies thedivided signal to the down counter 136 and supplies the divided signalto the down counter 137 by way of the AND gate 140.

Each of the down counters 136, 137 has an internal counter. The downcounters 136, 137 down count the count value by 1 and output “1” whenthe count value becomes “0”, while outputting “0” when the count valueis other than “0”. When a preset enable input is “1”, their count valuesare set to the settings K3, K4 which are set in the recording device 138under control of the CPU 27. The binary signal outputted from the downcounter 136 is supplied to the phase comparator 132 and is used as thepreset enable input for the down counters 136, 137. On the other hand,the binary signal outputted from the down counter 137 is not onlysupplied to the pulse swallow counter 135 but also supplied to aninverter 139 for providing an inverted signal to be supplied to the ANDgate 140 for obtaining the logical product of the inverted signal fromthe inverter 139 and the output from the pulse swallow counter 135. Thelogical product from the AND gate 140 is supplied to the down counter137.

The down counter 136 down counts the internal counter in such a manneras K3, K3−1, . . . , 0. When the count value of the down counter 136becomes “0”, “1” is supplied to the preset enable input of each of thedown counters 136 and 137, thereby returning the count values of thedown counters 136, 137 to K3 and K4, respectively. On the other hand,the down counter 137 down counts the internal counter in such a manneras K4, K4−1, . . . , 0. It continues to output “0” until before thecount value reaches “0”. When the count value of the down counter 137reaches “0”, the AND gate 140 outputs “0” and the then the count valueof the down counter 136 becomes “0”. As a result, the down counter 137stops with the count value “0” and the output “1” until the count valueis returned to K4. The binary signal outputted from the down counter 137acts as a signal for switching the dividing ratio of the pulse swallowcounter 135 to 1/K2 or 1/(K2+1). By the above-mentioned series ofoperations of the down counters 136, 137 and the pulse swallow counter135, the output of the down counter 136 is equal to 1/(K2×K3+K4) of theoutput from the VCO 134.

The recording device 138 holds at least four settings K1, K2, K3 and K4set by the CPU 27. As described hereinabove, the setting K1 held in therecording device 138 is used for determining the dividing ratio of thedivider 131, the setting K2 is used for determining the dividing ratioof the pulse swallow counter 135, the setting K3 is used for determiningthe dividing ratio of the down counter 136 and the setting K4 is usedfor determining the dividing ratio of the down counter 137.

In the frequency synthesizer 19 as described hereinabove, the foursettings K1, K2, K3 and K4 are not fixed values but can be variableunder control of the CPU 27. In the frequency synthesizer 19, the localoscillation frequency Flo of the local oscillation signal D10, i.e., thefrequency of the oscillation signal generated by the VCO 134 is equal to(K2×K3+K4) times the reference clock frequency.

In this manner, the frequency synthesizer 19 can generate the localoscillation signal D10 of variable frequencies to provide intermediatefrequencies Fif, e.g., 4.069 MHz±500 kHz or 1.023 MHz±500 kHz for theabove-mentioned amplified RF signal D8 having a particular frequencyFrf, i.e., 1575.42 MHz It is to be noted that, in case of performingdirect base band processing of the amplified RF signal D8 withoutcarrying out down converting, it is possible to generate the localoscillation signal D10 having the intermediate frequency Fif of 0MHz+500 kHz. Also, upon making it variable the frequency Frf to be downconverted into the intermediate frequency Fif within the variable rangeof the VCO 134, it becomes possible for the portable phone device 10 tosupport a plurality of radio waves.

It is to be noted that the frequency synthesizer 19 can be constructedto set the settings K1, K2, K3 and K4 by integrated circuit terminals orby way of an external interface rather than by the recording device 138under control of the CPU 27.

It is to be noted that, in the portable phone device 10, theintermediate frequency Fif is determined based on the local oscillationsignal D10 generated in accordance with the settings of such frequencysynthesizer 19. As a result, in the portable phone device 10,characteristics such as the pass band frequency and the like are madevariable, if necessary, under control of the CPU 27 so that thecharacteristic of the LPF 22 in the above-mentioned frequency conversionportion 24 is in compliance with the intermediate frequency Fif.

The LPF 22 may be either an analog filter or a digital filter. In theportable phone device 10, in case of utilizing a digital filter as theLPF 22, characteristics such as the frequency band and the like can beeasily programmable by using, e.g., an A/D and a DSP. Also, in theportable phone device 10, even in case of using an analog filter as theLPF 22, characteristics can easily be made variable by the constructionof selective switching a plurality of capacitors and resistors by usinganalog switches. It is to be noted in the portable phone device 10 thatthe LPF 22 can be replaced by a BPF without losing the variablecapability.

Subsequently, a basic technique of making it variable the settings inthe base band processing portion will be described.

In the portable phone device 10, the oscillation frequency Foscoscillating by the TCXO 13 is not specified to a particular value toallow a frequency range of, e.g., 10 to 20 MHz. In this way, the TCXO 13is shared as the operation clock for the frequency conversion portion24, the NCOs 104, 127 provided in the Costas loop 101 and the DLL 102 inthe base band processing portion and as the operation clock of the NCOwhich will be described hereinafter to be used as the sampling clock forthe sampler 71 in the synchronization capture portion 26.

As the synchronization hold portion 26 in the base band processingportion in the portable phone device 10, utilized is what is providedwith the NCOs 104, 127 in the Costas loop 101 and the DLL 102. As aresult, it is required in the Costas loop 101 to adjust the operationclock for the NCO 104 near the intermediate frequency Fif whileadjusting the operation clock for the NCO 127 in the DLL 102 near 1.023MHz which is substantially the chip rate of the C/A code.

Then, in the portable phone device 10, the dividing ratios of the NCOs104, 127 are made variable. At this event, in the portable phone device10, taking the oscillation frequency Fosc of the TCXO 13 and thenecessary frequency bandwidth into consideration, the dividing ratios ofthe NCOs 104, 127 are made adjustable by integrated circuit terminals,by the CPU 27 or by way of an external interface.

Also, in the portable phone device 10, characteristics such as the passband frequency and the like in the Costas loop 101 are made variable ifnecessary.

In the portable phone device 10, the LPFs 107, 108 are constructed,e.g., as shown in FIG. 9 in order to make their bandwidths variable. Itis assumed in FIG. 9 that the input signal is 1 bit. Since the receivingsignals from GPS satellites are considerably lower level than thermalnoise in the portable phone device 10, there is only slight degradationin S/N even if the analog/digital conversion is made in a binary form.

FIG. 9A shows an LPF which is an infinite impulse response filter forsubtractive approximation of the transfer function of an RC filter asshown in FIG. 9B. The LPF includes a multiplier 141 for multiplying aninput signal X[n] by the k-th power of 2, a multiplier 142 formultiplying a signal Y[n−1] supplied from a register 145 which will bedescribed hereinafter by the k-th power of 2, a subtracter 143 forobtaining subtraction of the signal Y[n−1] supplied from the register145 and the signal kY[n−1] from the multiplier 142, an adder 144 foradding the signal kY[n−1] from the multiplier 142 and the signal(1−k)Y[n−1] obtained by the subtracter 143 and the register 145 forholding a predetermined bits of the signal represented by thesubtractive approximation of the RC filter which is obtained by theadder 144. It is to be noted that the [n] in the input signal X[n] andthe output signal Y[n] represents dispersing time.

In such LPF, the relationship between the input signal X[n] and theoutput signal Y[n] is given by the following expression:Y[n]=(1−k)Y[n−1]+kX[n]The output signal from the adder 144 satisfies the above relationship.In the LPF, if a sampling frequency is fs, a time constant tc and acut-off frequency can be given by the following expressions:tc=RC=1/(kfs)fc=1/(2πRC)=kfs/(2π)k=1/(RCfs)As a result, if it is assumed in the LPF that k=2⁻¹⁶ and the samplingfrequency fs=18.414 MHz, the time constant tc is 3.56 milliseconds andthe cut-off frequency fc is 44.7 Hz.

In such LPF, the input signal X[n] is 1 bit and its value is either “1”or “−1”. However, if it is assumed in the input signal X[n] and theoutput signal Y[n] that the length of the register 145 is M bits, “1” is“100 . . . 0” and “−1” is “000 . . . 0” and also k is 2^(−L) (where, Lis an integer), the multiplier 141 for calculating kX[n] can be realizedby a barrel shifter for performing left shift of (M-L) bits, while themultiplier 142 for calculating kY[n] can be realized by a barrel shifterfor performing right shift of L bits. For example, in case of theregister 145 having the length of 22 bits and the k=2⁻¹⁶, the multiplier141 can be realized by a barrel shifter for performing left shift of 6bits, while the multiplier 142 can be realized by a barrel shifter forperforming left shift of 16 bits. As a result, in the LPF, if the L canbe set externally, the cut-off frequency fc can be varied in the unit ofoctave. Also, in the LPF, if “0” is deemed to be “010 . . . 0”, sign ofthe output signal Y[n] can be judged by comparing with the relative sizewith the above value. Moreover, in the LPF, by outputting the series ofbits held in the register 145 excluding the MSB and inverting the MSBbit of the remaining bits, the output signal Y[n] will be the complementof 2.

In the portable phone device 10 having the LPFs 107, 108 of the aboveconstruction, if the value of the above-mentioned k is made adjustableby the CPU 27 or by way of an external interface, it is possible toeasily set the bandwidth in consideration of the oscillation frequencyFosc of the TCXO 13. It is to be noted in the portable phone device 10that bandwidths of the LPFs 117, 118, 122 and 123 in the DLL 102 arepreferably variable and these LPFs 117, 118, 122 and 123 are constructedas shown in FIG. 9.

Moreover, in the portable phone device 10, characteristics of the loopfilters 109, 126 for controlling phases of the NCOs 104, 127 in theCostas loop 101 and the DLL 102 are designed to be variable ifnecessary.

In the portable phone device 101, these loop filters 109, 126 can beconstructed similar to the LPF as shown in FIG. 9. However, they canalso be constructed as a complete integration type loop filters whichare optimum filters in case of presence of frequency offset and randomphase offset.

FIG. 10A shows an equivalent circuit of a complete integration type loopfilter as shown in FIG. 10B. The transfer function F(s) in the loopfilter can be given by the following expression:F(s)=(1−sτ2)/(sτ1), τ1=R1C, τ2=R2CBy subtractive approximation; the relationship between the input signalX[n] and the output signal Y[n] can be given by the followingexpression:Y[n]=Y[n−1]+a(X[n]−X[n−1])+bX[n]a=τ2/τ1, b=T/τ1Where, T is the period of a sampling frequency and the samplingfrequency is set sufficiently higher than the cut-off frequency of theLPF. As apparent from the above expression, there are two parameters aand b adjustable in the loop filter. Let these parameters a and b berespectively a=2^(A) and b=2^(B) (A and B are integers), the aX[n],aX[n−1] and bX[n] can be calculated through simply shifting A bits or Bbits to left, respectively. This means that the calculation as shown inthe above expression may be realized through a loop filter as shown inFIG. 11.

As a result, in the loop filter, if the values A and B are set by theCPU 27 or by way of an external interface, the bandwidth and theresponse speed of the loop filter can be changed in accordance with thereceiving condition.

Furthermore, in the portable phone device 10, the NCO is utilized, ifnecessary, as means for generating the sampling clock for the sampler 71in the synchronization capture portion 25, thereby also changing thefrequency range of the NCO.

In other words, the sampler 71 in the synchronization capture portion 25is required to perform sampling 2046 points or more of the IF signal in1 millisecond equal to 1 period of the C/A code. For this end, asdisclosed in the specifications of Japanese patent application nos.2001-190658 and 2001-203193 filed by the assignee of this patentapplication, the synchronization capture portion 25 is convenientlyperforming FFT processing with sampling number equal to a power of 2.For this reason, the sampler 71 for sampling the IF signal in thesynchronization capture portion 25 is constructed by using the NCO whichoperates based on the oscillation signal D2 supplied from the TCXO 13.And the dividing ratio of the NCO is made to be variable by the settingof integrated circuit terminals, the CPU 27 or by way of an externalinterface in a similar manner as the Costas loop 101 and the DLL 102,thereby enabling to obtain any desired sampling clock.

As it may be understood from the above description, in the portablephone device 10, the operation clock is shared by at least the frequencysynthesizer 19 in the frequency conversion portion 24 and the NCOs 104,127 in the Costas loop 101 and the DLL 102. And the frequencysynthesizer 19 and the NCOs 104, 127 are designed to be set variable byintegrated circuit terminals, by the CPU 27 or by way of an externalinterface. In addition, if necessary, various digital filters or analogfilters such as the LPFs 107, 108, 117, 118, 122 and 123 in the Costasloop 101 and the DLL 102 as well as the loop filters 109, 126 in theCostas loop 101 and the DLL 102 and the NCO to be provided in thesampler 71 in the synchronization capture portion 25 are constructed tobe set variable by integrated circuit terminals, by the CPU 27 or by wayof an external interface, thereby enabling to assemble the GPS receivingfunction which is unaffected by the oscillation frequency Fosc of theTCXO 13. In addition, the common use of the telephone unit 11 and theTCXO 13 in the portable phone device 10 enables to reduce the number ofthe necessary oscillators.

Now, concrete descriptions of the above described various portions withvariable settings and other portions will be given hereunder.

Firstly, a description will be given about the frequency conversionportions 24.

The LPF 22 (which may be replaced by a BPF) is most likely to beconstructed as an analog design, thereby providing a fixedcharacteristic. In the portable phone device 10, since thecharacteristics such as the pass band frequency and the like of the LPF22 is determined in matched with the intermediate frequency Fif, thedemodulation circuit 31, i.e., the GPS unit is designed in theconstruction as shown in FIG. 1. And the dividing ratio of the frequencysynthesizer 19 in the frequency conversion portion 24 is set so that theintermediate frequency Fif remains substantially the same frequencyregardless of the oscillation frequency Fosc of the TCXO 13, therebyavoiding any problem. It is to be noted in the portable phone devicethat the range of the intermediate frequency Fif may be in a certainrange within the bandwidth from the fixed characteristic LPF 22 point ofview. In order to set the range of the intermediate frequency Fif toremain near the intended value regardless of the oscillation frequencyFosc of the TCXO 13, the above mentioned setting K1 is set sufficientlylarge and the reference clock frequency for performing phase comparisonin the phase comparator 132 is decreased.

In the frequency synthesizer 19 as shown in FIG. 8, in a case when theoutput of the TCXO 13 having the oscillation frequency Fosc of 18.414MHz is used as the reference clock and the above-mentioned settings K1,K2, K3 and K4 are respectively set to 18, 100, 14 and 39, theintermediate frequency Fif is equal to 1.023 MHz. On the other hand, ina case when the settings K1, K2, K3 and K4 are respectively set to 20,100, 31 and 49, the intermediate frequency Fif is equal to 0.92 MHz. Inthis case, the difference in the intermediate frequencies isapproximately 100 kHz, thereby causing no considerable difference inperformance between them in the portable phone device 10 which utilizesa normal LPF as the LPF 22.

It is also normal that the frequency synthesizer 19 is provided as ananalog signal processing portion rather than a digital signal processingportion including base band processing, a CPU and the like. However, thedivider itself is performing digital signal processing. As a result, bydividing each divider in accordance with the settings set by theabove-mentioned register 138, it is possible to set the dividing ratiovariable by the CPU 27 or by way of an external interface.

It is to be noted that the settings of the register 138 in the portablephone device 10 are carried out by integrated circuit terminals, by theCPU 27 or by way of an external interface as described hereinabove.However, in a case where the number of bits of the settings is large,pin counts for making connection between the frequency conversionportion 24 including the frequency synthesizer 19 and the base bandprocessing portion including the CPU 27 increase, which is not desirablein fabricating as an integrated circuit. As a result, in case of readingout and writing the settings of the register 138 by the CPU 27 in theportable phone device 10, it is possible to decrease the necessary pincounts for making connection between the frequency conversion portion 24including the frequency synthesizer 19 and the base band processingportion including the CPU 27 by performing serial transmission based ona predetermined communication protocol.

In the following, the NCO 127 provided in the DLL 102 in the base bandprocessing portion will be described hereunder.

In the portable phone device 10, since the RF signal is the spreadspectrum signal, the DLL 102 for synchronizing the spread code isdesigned to set the dividing ratio in accordance with the oscillationfrequency Fosc of the TCXO 13 so that the NCO 127 covers near 1.023 MHzwhich is the chip rate of the C/A code, i.e., the spread code. The NCO127 can be constructed, e.g., as shown in FIG. 12.

In other words, as shown in FIG. 12, the NCO 127 includes dividers 151,152 for dividing the oscillation signal D2 supplied from the TCXO 13 byrespectively predetermined dividing ratios, a register setting portion153 for setting the K-bit register value representing the resolution ofthe value held in a register 155 which will be described hereinafter, anadder 154 for cumulatively adding the register value set in the registersetting portion 153 and the read-out value from the register 155, thelimited length register 155 for holding the cumulatively added valuesupplied from the adder 154, a divider 156 for dividing the dividedoscillation signal supplied from the divider 152 by a predetermineddividing ratio and a recording device such as a register, a memory andthe like for holding settings N, M1, M2 and M3 set by the CPU 27.

The divider 151 divides the oscillation signal D2 supplied from the TCXO13 by the dividing ratio 1/M1 represented by the setting M1 in therecording device 157 under control of the CPU 27. The divider 151supplies the divided signal to the register 155.

The divider 152 divides the oscillation signal D2 supplied from the TCXO13 by the dividing ratio 1/(M2−1), 1/M2 or 1/(M2+1) represented by thesetting M2 in the recording device 157 under control of the CPU 27 inaccordance with the read-out value of the register 155. The divider 152supplies the divided signal to the divider 156.

Set in the register value setting portion 153 is a setting N set by thememory device 157 under control of the CPU 27 as a K-bits register valuerepresenting the resolution of the value held in the register 155. Theregister value N is represented by a complement of 2 and takes bothpositive and negative values. The register value N set by the registervalue setting portion 153 is supplied to the adder 154.

The adder 154 adds the register value N set by the register valuesetting portion 153 and the read-out value of the register 155. Theadder 154 supplies the cumulatively summed value to the register 155. Asa result, the value held in the register 155 is the cumulative sum ofthe register values N.

The register 155 has a K-bits limited length register and holds thecumulative sum from the adder 154 based on the timing of a gate signal.The value of the cumulative sum hold by register 155 is used fordetermining the dividing ratio of the divider 152.

The divider 156 divides the oscillation signal supplied from the divider152 by the dividing ratio 1/M3 represented by the setting M3 set by therecording device 157 under control of the CPU 27. The divider 156outputs the divided signal as a reproduced carrier.

The recording device 157 holds four settings N, M1, M2 and M3 set by theCPU 27. As described hereinabove, the setting N held in the recordingdevice 157 is used as the register value set in the register valuesetting portion 153. The setting M1 is used for determining the dividingratio of the divider 151. The setting M2 is used for determining thedividing ratio of the divider 152. The setting M3 is used fordetermining the dividing ratio of the divider 153.

Such NCO 127 sets the four settings N, M1, M2 and M3 as variable valuesunder control of the CPU 27 rather than fixed values. In this way, sincethe register 155 in the NCO 127 is a limited length register, there isan instance when an overflow takes place. In case of cumulativelysumming the register values N set in the register value setting portion153 in the NCO 127, if no overflow takes place in the value held in theregister 155, the dividing ratio of the divider 152 is 1/M2. However, ifoverflow takes place, a counter (not shown) in the divider 152 counts upmore than M2 by “1”, thereby setting the dividing ratio to 1/(M2+1). Ifa negative overflow takes place, the divider 152 counts up less than M2by “1”, thereby setting the dividing ratio to 1/(M2−1). Consequently,the NCO 127 outputs the reproduced carrier having the frequency equal to1/(M2×M3) times of the oscillation frequency Fosc supplied from the TCXO13, if the register setting value N=0 set by the register value settingportion 153. It outputs the reproduced carrier having a higher frequencythan the case when the register value N=0, if the register value N>0. Onthe other hand, it outputs the reproduced carrier having a lowerfrequency than the case when the register value N=0, if the registervalue N<0.

Also, the frequency range of the NCO 127 is set to cover the range ofthe chip rate of the spread code in addition to the error in theoscillation frequency Fosc of the TCXO 13 and the Doppler shift valuecaused by the changes of the relative movement of the GPS satellite atthe transmitter side and the receiver side. For example, in the portablephone device 10 using the TCXO 13, in which the error in the oscillationfrequency is approximately ±3 ppm or less and the Doppler shift value isapproximately ±3 ppm or less, it is sufficient if the variable range ofthe NCO 127 is at least approximately 1.023 MHz±6 ppm.

In addition, the NCO 104 provided in the Costas loop 101 in the baseband processing portion will be described as follows.

The RF signal is a signal in which the modulation signal modulated by,e.g., binary phase shift keying modulation system (referred to as BPSKmodulation system below) or the modulation signal based on the PSKmodulation system is a spread spectrum signal. However, the Costas loop101 for synchronizing the carrier of the PSK signal in the IF signal isdesigned to set the dividing ratio in accordance with the oscillationfrequency Fosc of the TCXO 13 so that the NCO 104 covers near theintermediate frequency Fif of 1.023 MHz, e.g., by the setting of thefrequency conversion portion 24. It is to be noted here that the NCO 104can be constructed in the same way as the NCO 127 as shown in FIG. 12.

Similar to the NCO 127, the frequency range of the NCO 104 is set tocover the area of the intermediate frequency Fif in addition to theerror of the oscillation frequency Fosc of the TCXO 13 and the Dopplershift aalue caused by the relative speed of the GPS satellite at thetransmission side and the receiver side. For example, as describedhereinabove, if the TCXO 13 is used in the portable phone device 10 andif the oscillation frequency error is approximately ±3 ppm or less, theDoppler shift aalue is approximately ±3 ppm or less. As a result, incase of converting the carrier signal frequency Frf of the RF signalinto the intermediate frequency Fif by the frequency conversion portion24 at one time in the portable phone device 10, if the local oscillationfrequency Flo is L (integer) times the reference clock frequency of thefrequency synthesizer 19, the error of the intermediate frequency Fifdue to the error in the oscillation frequency Fosc of the TCXO 13becomes L times. This means that the variable range of the NCO 104 canbe those including at least 1.023 MHz±3L ppm±3 ppm.

In addition, the sampler 71 provided in the synchronization captureportion 25 in the base band processing portion will be describedhereunder.

In the portable phone device 10, in the case in which thesynchronization capture portion 25 is constructed as shown in FIG. 3 andthe synchronization capture portion 25 performs the digital matchedfilter processing for establishing synchronization with the spread codeof the spread spectrum signal, it is necessary to acquire 2046 or moreinteger samples of the IF signal by the sampler 71 in 1 millisecondwhich is 1 period of the C/A code as described hereinabove. The samplingclock for sampling the IF signal is generated based on the oscillationfrequency Fosc of the TCXO 13 in the portable phone device 10, if thesampling frequency is different because of different oscillationfrequency Fosc, it becomes difficult to perform digital matched filterprocessing.

However, in the portable phone device 10, the sampler 71 is constructedby using the similar construction to the NCO 127 as shown in FIG. 12 forgenerating the sampling clock. And the NCO is set in such a manner thatthe number of samples in 1 millisecond remains a constant integer, i.e.,the sampling rate is constant in accordance with the oscillationfrequency of the TCXO 13. In this manner, the portable phone device 10is not affected by the oscillation frequency Fosc of the TCXO 13 and thedigital matched filter processing can be performed in the sameprocedure, e.g., in case of software processing.

It is to be noted that, in case of generating the sampling clock simplyby the NCO only, because of the relationship between the oscillationfrequency Fosc of the TCXO 13 and the frequency resolution of the NCO,e.g., as shown at the second column in FIG. 13, there may cause afraction in the number of samples in 1 period of the spread codedepending on the length of sampling time. This phenomenon is notdesirable in case of performing signal processing over plural periods ofthe spread code. In order to avoid such phenomenon, it is necessary tosignificantly increase the frequency resolution of the NCO.

In view of this, in the portable phone device 10, a periodic timingreset signal in form of a pulse is generated substantially correspondingto 1 period of the spread code by predetermined timing signal generationmeans, e.g., as shown at the first column in FIG. 13. The samplingtiming is initialized by operating the dividers 151, 152 and 156 and theregister 155 as shown in FIG. 12 which constitutes the NCO in thesampler 71 for generating the sampling clock as shown at the thirdcolumn in FIG. 13 so that they are reset at every period by the timingreset signal. As a result, in the portable phone device 10, the numberof samples in 1 period of the spread code always remains constant andthe timing for performing the sampling is maintained substantiallyidentical in each period. Although there may cause unevenness insampling intervals at the very last part of each period due to afraction in 1 period of the spread code, there is no need to choose anextremely high frequency resolution for the NCO because the samplingtiming is corrected at every period.

It is to be noted that, in the portable phone device 10, the leastsignificant digit of the oscillation frequency Fosc of the TCXO 13 isdetermined in accordance with the period of the C/A code, or the spreadcode. Describing in other words, since the period of the C/A code, orthe spread code is 1 millisecond in the portable phone device 10, if theleast significant digit of the oscillation frequency Fosc of the TCXO 13is 1 kHz, the NCO can easily generate a periodic timing reset signalsubstantially equal to 1 period. Also, in the portable phone device 10,such processing can be performed easily because the timing reset signalis generated at the interval of 1 millisecond which is equal to 1 periodof the spread code, i.e., 1 kHz. As a result, in the portable phonedevice 10, it is possible to give freedom within a certain range in theoscillation frequency Fosc of the TCXO 13 and specifying 1 kHz as itsleast significant digit and to easily generate the timing reset signalat the interval of 1 millisecond by the NCO including a divider havingthe dividing ratio 1/18414 in the case in which the oscillationfrequency Fosc of the TCXO 13 is 18.414 MHz.

Although the least significant digit of the oscillation frequency Foscwas 1 kHz in the above description, it is possible that the leastsignificant digit of the oscillation frequency Fosc in the portablephone device 10 could be 1 kHz divided by any integer number. In thiscase, the portable phone device 10 can generate the timing reset signalat an interval equal to 1 millisecond multiplied by an integer. Forexample, if the oscillation frequency Fosc is 18.4145 MHz, the use ofthe NCO including the divider of the dividing ratio equal to 1/336829makes it possible to generate the timing reset signal at the interval of2 milliseconds which is two periods long of the C/A code. In this case,in the portable phone device 10, the above-mentioned processing formaintaining the constant number of samples in 1 period of the spreadcode can be replaced from 1-period length to 2-period length, therebyenabling to perform the processing such as FFT and the like in the2-period long data unit. Alternatively, the data is split into 2 halvesto be processed in a 1 period length, which, as a result, may slightlyincrease contents of the processing, but helps to ease the processing byperforming at the unit of the period of the C/A code.

In addition, in case of performing the digital matched filter processingin the portable phone device 10 by utilizing FFT as shown in FIG. 2,since it is convenient for FFT processing that the number of samples isequal to a power of 2, the processing can be made very easily by settingthe sampler 71 to acquire samples equal to a power of 2 in 1 period ofthe spread code.

Moreover, in the portable phone device 10, if the spread code is aso-called M series or a so-called Gold code generated from the M serieswhich has the code length equal to (a power of 2-1), it is sometimeseasier to acquire the number of samples equal to (a power of 2-1) in 1period of the spread code depending on the oscillation frequency Fosc ofthe TCXO 13. If the digital matched filter processing utilizes FFT asshown in FIG. 2, it is preferable that the number of samples is equal toa power of 2. In case of processing the spread code having the codelength equal to (a power of 2-1) in the portable phone device 10, dummybits are inserted into 1 period of the spread code at a constantinterval for adjusting the number of data to be FFT processed equal to apower of 2.

For example, in case of performing the sampling to acquire 4096 samplesin 1 millisecond equal to 1 period of the C/A code in the portable phonedevice 10, 1 dummy data is inserted at every ¼ period or 1023 samples.At this event, the dummy data to be inserted is in general the same asthe bit immediately preceding the dummy data, but may be a fixed bit.

It is to be noted that, if there is a marginal processing capacity incase of installing the digital matched filter processing in the portablephone device 10, it is not necessarily to adjust the number of samplesin 1 period of the spread code equal to a power of 2 even if performingFFT processing. The NCO in the sampler 71 is set to acquire slightlymore samples which are thinned down to be equal to a power of 2 bysoftware processing before performing FFT processing on the thinned downdata.

Then, a description will be given on each filter including the LPF inthe base band processing portion or the frequency conversion portion 24.

In the case in which the LPF is constructed as the digital filter, e.g.,as shown in FIG. 9A, the bandwidth of the LPF may be set under multiplesteps. In the LPF as shown in FIG. 9, if the sampling frequency is fs asdescribed hereinabove, the time constant tc and the cut-off frequency fccan be given by the following expressions:tc=RC=1/(kfs)fc=1/(2πRC)=kfs/(2π)k=1/(RCfs)If it is assumed that the sampling frequency fs and the oscillationfrequency Fosc of the TCXO 13 are equal to each other, the cut-offfrequency fc changes in proportion to the oscillation frequency Fosc ofthe TCXO 13.

As a result, if such LPF is applied to the Costas loop 101 as shown inFIG. 5 and if the sampling frequency fs=20 MHz, the cut-off frequency fcis equal to 48.6 Hz. On the other hand, if the sampling frequency fs=10MHz, the cut-off frequency fc is equal to 24.3 Hz. It is assumed herethat the data transmission rate is 50 bps and the main bandwidth of themessage contained in the signal, which is an NRZ (Non Return to Zero)signal, from the GPS satellite is 25 Hz, the above-mentioned 24.3 Hzwhich is the cut-off frequency fc in case of the sampling frequencyfs=10 MHz is slightly narrow. As a result, if the sampling frequencyfs=10 MHz in the portable phone device 10, the cut-off frequency fc isincreased by 1.

In addition, it is possible in the portable phone device 10 to utilizeas the LPF a finite impulse response (FIR) filter as shown in FIG. 9(A)and an IIR filter of another construction. It is also possible in theportable phone device 10 to provide an LPF at the following stage of theA/D 23 in the frequency conversion portion 24 as shown in FIG. 1 inportions other than the Costas loop 101, thereby constituting the LPF asa digital filter. Moreover, it is possible to apply a BPF having thebandwidth centered near the intermediate frequency Fif instead of theLPF in the portable phone device 10. In the portable phone device 10 towhich either the LPF or the BPF is applied, since the frequency band ofthe filter changes depending on the oscillation frequency Fosc of theTCXO 13 by constructing the frequency synthesizer 19 so that theintermediate frequency Fif remains within a substantially constantrange, it is effective in this case to make the frequency band of suchfilter variable.

In the portable phone device 10 according to the above construction, thefilter is designed to have a variable frequency bandwidth so that thefilter can operate with the optimum frequency band depending on theoscillation frequency Fosc of the TCXO 13.

It is to be noted that, as described hereinabove, the portable phonedevice 10 perform the position calculation by measuring thesynchronization timing of the C/A code which is the spread code of 1millisecond period in the spectrum spread signals from the GPSsatellites, thereby acquisition of the own position. At this event, thetime resolution in measuring the synchronization timing of the spreadcode depends on the operation clock frequency of the synchronizationcircuit such as the above-mentioned synchronization capture portion 25.As a result, in case of generating the operation clock in thesynchronization circuit in the portable phone device 10, time resolutionin such measurement depends on the operation frequency Fosc of the TCXO13.

In general, in the GPS receiver, a measurement is made based on thereference timing as a reference point in synchronism with a clockprovided within the GPS receiver and counting the delay time of the headof C/A code from the reference point by a counter, thereby calculatingthe pseudo-distance which is the distance that the radio wave traveledfrom the GPS satellite to the GPS receiver based on the clock of the GPSreceiver as a reference. It is to be noted that the count value differsdepending on the oscillation frequency of the TCXO 13 even if the radiowave arrived at a same time.

In view of this, the portable phone device 10 converts the count valueinto time in accordance with the oscillation frequency Fosc of the TCXO13 under control of the CPU 27 as shown in FIG. 1. This enables toeasily cope with calculation of the pseudo-distance even if theoscillation frequency Fosc of the TCXO 13 is changed.

Up to now, the above description has been directed to a demodulationcircuit of the spectrum spread signal including the signal from the GPSsatellite and demodulation in the GPS receiver. However, the portablephone device 10 may include measures for the oscillation frequency Foscof the TCXO 13 in the portions other than what are describedhereinabove.

In general, the GPS receiver includes, e.g., various input/outputinterfaces such as a predetermined serial port, a USB (Universal SerialBus) port and the like and various peripherals such as a control timersuch as the above-mentioned timer 29, an A/D, a digital/analog converter(referred to as D/A below) and the like in order to communicate withexternal devices. In the GPS receiver, it is normal that the operationclocks for these various portions are generated from the same sourceoscillator for various portions for performing frequency conversion andsynchronization.

In view of this, in the portable phone device 10, since the oscillationfrequency Fosc of the TCXO 13 affects the communication speed, time, thesampling frequency and the like, settings of the communication speed ofvarious input/output interfaces, the timer 29 and the sampling frequencyof the A/D and the D/A are changed in accordance with the oscillationfrequency Fosc. As a result, various peripherals in the portable phonedevice 10 are made to operate regardless of the oscillation frequencyFosc of the TCXO 13.

As apparent from the above description, in the portable phone device 10,the oscillator required for the GPS unit and the TCXO 13 which is ingeneral provided for the telephone unit 11 are made to common andsettings for various portions are changed in accordance with theoscillation frequency Fosc of the TCXO 13, thereby making it independentof any change in the oscillation frequency Fosc. This eliminates theneed of an oscillator exclusively for the GPS unit, thereby reducing thenumber of oscillators. In other words, even if a source oscillator notoscillating particular frequencies are utilized, the portable phonedevice 10 can be operated regardless of the change in the oscillationfrequency by changing the settings of various portions in accordancewith the oscillation frequency of the source oscillator, therebyreducing the number of oscillators.

It is to be noted that, in case of installing a wireless unitcorresponding to a predetermined wireless system such as, e.g.,so-called Bluetooth (a trademark), a wireless LAN (Local Area Network)and the like in addition to the telephone unit 11 in the portable phonedevice 10 in the same module or apparatus, there is an oscillator foroscillating the frequency in accordance with the type of wireless towhich the wireless unit responds for the wireless unit or signalprocessing. In this case, in the portable phone device 10, theoscillator provided for the wireless unit or the signal processing maybe used as the source oscillator. As a matter of course, in case ofinstalling a unit for realizing functions other than tat of the wirelessunit in the portable phone device 10, it is possible to use theoscillator provided for the unit may be the source oscillator for theGPS unit.

It is to be noted that, in the portable phone device 10, settings thatare changed in accordance with the oscillation frequency Fosc of theTCXO 13 are for at least the dividing ratio of the frequency synthesizer19 in the frequency conversion portion 24 and the frequency range of theNCOs 104, 127 in the Costas loop 101 and the DLL 102 as describedhereinabove, however it may be also for characteristics of variousfilters such as the LPF, the sampling clock of the sampler 71 in thesynchronization capture portion 25 and other various peripherals, ifsuch a need arises. In this manner, there are many portions requiringfor changing the settings in accordance with the oscillation frequencyFosc of the TCXO 13 in the portable phone device 10. As a result, in theportable phone device 10, it is complicated to calculate optimumsettings for various portions and to set each obtained setting by way ofa predetermined external interface and the like.

Therefore, in the portable phone device 10, the routine for calculatingeach setting in accordance with the oscillation frequency Fosc of theTCXO 13 is installed in a program executed by the CPU 27. Upon inputtingonly the oscillation frequency Fosc of the TCXO 13 from the externalinterface, the CPU 27 can calculate each setting based on the inputoscillation frequency Fosc. Subsequently, the CPU 27 automatically setseach setting to the respective portion, thereby overcoming complicatedprocedure to set.

Also, in the portable phone device 10, when an oscillator of anotherknown frequency such as the above-mentioned XO 12 for generating anoscillation signal of a predetermined frequency in the range of, e.g.,about 32.768 kHz for supplying the operation clock for theabove-mentioned RTC 28, it is possible to provide a function to simplycount the output pulse from the TCXO 13 acting as the source oscillatorfor a given time interval by using the oscillation signal generated bythe oscillator as a gate signal, thereby enabling the portable phonedevice 10 to recognize the approximate oscillation frequency Fosc basedon the count value. Specifically, assuming that accuracy of the XO 12 istentatively ±100 ppm in the portable phone device 10, for the TCXO 13permitting the frequency range of, e.g., approximately 10 to 20 MHz, theoscillation frequency Fosc of the TCXO 13 can be estimated in theaccuracy of approximately ±100 ppm, i.e., approximately ±1 to 2 kHzerror range. Also, in the portable phone device 10, if the accuracy ofthe XO 12 is better than the above, it can well identify the oscillationfrequency of the TCXO 13 in the unit of 1 kHz.

Since oscillation frequencies of shared source oscillators are actuallylimited, if it is possible to estimate the approximate values, a tableof the oscillation frequencies Fosc, e.g., available TCXO 13 is storedin the memory 30 in advance, thereby enabling to surely determine theoscillation frequencies of the oscillators. As a result, in the portablephone device 10, such function is installed as an initial routine of theCPU 27 so that it is initiated as soon as the power of the portablephone device 10 is turned on. When the CPU 27 identifies the oscillationfrequency of the TCXO 13, it is possible to automatically set thefrequency synthesizer 19 in the frequency conversion portion 24, filterssuch as NCOs 104, 127, LPF and the like in the Costas loop 101 and theDLL 102, the sampler 71 in the synchronization capture portion 25 andvarious other peripherals by combining the above-mentioned settingoperation for various portions by the CPU 27. It is to be noted that,since external control of the peripherals is difficult in the portablephone device 10 under condition in which the communication speed is notset, it is important to enable external communication by automaticallysetting the communication speed of the input/output interface with anexternal device.

As described hereinabove, in the GPS unit assembled in the portablephone device 10, since the necessary clock frequency is not necessarilya particular frequency, it is possible to utilize commercially availablestandard oscillators as the TCXO 13.

In addition, when assembling or embedding the GPS unit as a requiredsource oscillator in an electronic apparatus such as the portable phonedevice 10 and the like, it is possible to share the oscillator such asthe TCXO 13 and the like provided for the unit to realize other functionsuch as the telephone unit 11. This may eliminate the need for providingthe oscillator exclusively for the GPS unit, thereby permitting reducingthe number of oscillators to be installed in the electronic apparatusand also permitting realizing attempts at downsizing the apparatus.

Moreover, in case of fabricating in a module or an integrated circuitlike the above-mentioned demodulation circuit 31 to provide varioussource oscillators, i.e., the various oscillation frequencies Fosc ofthe TCXO 13, the GPS unit requires only a single type of module orintegrated circuit. As a result, the GPS units can be commercialized asgeneral purpose products which can be installed in electronicapparatuses having various oscillation frequencies.

Furthermore, the GPS unit can be applied to a plurality of differentwireless frequencies because the frequency Frf of the RF signal and thefrequency Fif of the IF signal is made variable.

It is to be noted that the present invention should not be restricted tothe above preferred embodiment of the present invention. For example,although the above preferred embodiment of the present invention isdescribed using the portable phone device 10 having the GPS unitassembled therein for achieving the function of the GPS receiver, thepresent invention can be easily applied to any electronic apparatusother than portable phone devices. Also, the present invention can beeasily applied to any electronic apparatus having units assembledtherein for achieving functions other than the GPS unit.

Although the above example of preferred embodiment of the presentinvention has been described as for demodulating the spectrum spreadsignal, the present invention can be applied to any signal other thanthe spectrum spread signal as long as predetermined high frequencysignals are demodulated.

In addition, although the above preferred embodiment of the presentinvention is described about the portable phone device 10 having the GPSunit assembled therein for achieving the function of the GPS receiver,the present invention can be applied to any electronic apparatus formeasuring position utilizing satellites, i.e., any electronic apparatushaving the function of the receiver to which the GNSS system is applied.The GNSS system is not restricted to the above-mentioned GPS system ofthe United States of America but can be the GLONASS (Global NavigationSatellites System) of the former USSR, the GALILEO under developmentmainly by European countries, and the like. The present invention may beapplied to any of these GNSS systems.

Finally, other changes, variations, combinations and sub-combinationsare possible in the present invention. Also, it is therefore to beunderstood that any modifications will be practiced otherwise than asspecifically described herein without departing from the scope andspirit of the present invention.

1. A demodulation apparatus for demodulating a high-frequency signalcomprising a spread spectrum signal, the apparatus comprising: frequencyconversion means for converting said high-frequency signal to anintermediate frequency; signal processing means for performing a signalprocessing on an intermediate-frequency signal having said intermediatefrequency obtained through said frequency conversion means; and settingmeans for performing settings on said frequency conversion means andsaid signal processing means; wherein said frequency conversion meansincludes local oscillation signal generation means for generating alocal-oscillation signal having a local oscillation frequency forconverting a frequency of said high-frequency signal into saidintermediate frequency based on a source oscillation signal generated bya source oscillator; said setting means counts said source oscillationsignal generated by said source oscillator using as a gate signal theoscillation signal generated by another oscillator of known frequencydifferent from said source oscillator and the setting means makes ajudgment of said source oscillation frequency of said source oscillationbased on said count value; and said signal processing means includessignal generation means for sharing said local oscillation signalgenerator means and said source oscillator and for generating a signalhaving a predetermined frequency based on said source oscillation signalgenerated by said source oscillator.
 2. The demodulation apparatusaccording to claim 1, wherein said local oscillation signal generationmeans makes said local oscillation frequency of said local oscillationsignal variable upon setting a dividing ratio variable by way of settingmeans in accordance with an arbitrary source oscillation frequency ofsaid source oscillation signal generated by said source oscillator, sothat said intermediate frequency remains within a predetermined rangeregardless of the source oscillation frequency of said sourceoscillation signal.
 3. The demodulation apparatus according to claim 1,wherein said signal generation means makes a frequency of said signalvariable by setting a dividing ratio variable by way of said settingmeans in accordance with an arbitrary source oscillation frequencygenerated by said source oscillator.
 4. The demodulation apparatusaccording to claim 1, wherein said setting means sets a setting value ofrespective dividing ratios of said local oscillation signal generationmeans and said signal generation means.
 5. The demodulation apparatusaccording to claim 2, wherein said signal processing means includes saidsetting means.
 6. The demodulation apparatus according to claim 2,wherein said local oscillation signal generation means and said signalgeneration means respectively include memory means for holding a settingvalue set by said setting means.
 7. The demodulation apparatus accordingto claim 6, wherein said setting means sets said setting value of saidmemory means upon performing serial transmission based on acommunication protocol.
 8. The demodulation apparatus according to claim1, wherein said signal processing means includes sampling means forsampling said intermediate frequency signal at a sampling frequencybased on said source oscillation signal generated by said sourceoscillator, and said sampling means makes said sampling frequencyvariable by setting a dividing ratio variable through said setting meansin accordance with an arbitrary source oscillation frequency of saidsource oscillation signal.
 9. The demodulation apparatus according toclaim 8, wherein said sampling means sets a dividing ratio variablethrough said setting means in accordance with said arbitrary sourceoscillation frequency of said source oscillation signal so that a numberof samples per period of spread code becomes a constant integer value.10. The demodulation apparatus according to claim 9, wherein saidsampling means generates a periodic timing reset signal substantiallymatching with 1 period of said spread code based on said sourceoscillation signal, and initializes the sampling timing based on saidtiming reset signal.
 11. The demodulation apparatus according to claim8, wherein the minimum unit of said source oscillation signal on saidsource oscillator is determined according to a period of said highfrequency signal.
 12. The demodulation apparatus according to claim 9,wherein said 1 period of the spread code of said high-frequency signalis 1 millisecond and the least significant digit of said sourceoscillation frequency is 1 kHz.
 13. The demodulation apparatus accordingto claim 9, wherein 1 period of the spread code of said high-frequencysignal is 1 millisecond; a least significant digit of said sourceoscillation frequency is 1 kHz divided by any integer number, and saidsampling means sets said dividing ratio variable through said settingmeans in accordance with said arbitrary source oscillation frequency ofsaid source oscillation signal so that a number of samples per period ofsaid source oscillation signal multiplied by any integer number becomesa constant integer number, rather than 1 period of said spread code. 14.The demodulation apparatus according to claim 13, wherein said samplingmeans sets a number of samples per period of said spread code by a powerof
 2. 15. The demodulation apparatus according to claim 9, wherein saidspread spectrum signal has a code length of a power of 2^(L), where L isan integer, and said sampling means sets the number of samples perperiod of said spread code to a power of 2^(L), where L is an integer,and a dummy bit is inserted at a constant interval into said period ofsaid spread code so that a number of data in 1 period of said spreadcode is a power of
 2. 16. The demodulation apparatus according to claim15, wherein said dummy bit has a value equal to an immediately precedingbit or a fixed value.
 17. The demodulation apparatus according to claim9, wherein said signal processing means decimates the data sampled bysaid sampling means so that the number of samples per period of saidspread code is a power of 2, and performs signal processing on thedecimated data.
 18. The demodulation apparatus according to claim 8,further comprising a synchronization capture means for performingsynchronization capture for detecting a phase of a spread code in saidintermediate frequency signal obtained by said frequency conversionmeans; and for detecting a carrier frequency in said intermediatefrequency signal; wherein said synchronization capture means includessaid sampling means.
 19. The demodulation apparatus according to claim1, wherein said frequency conversion apparatus and said signalprocessing means have respective filter means for passing frequencycomponents of respectively input signals, and said filter means forpassing frequency components of respective input signals, and saidfilter means sets characteristics including a pass band frequencyvariable by way of said setting means in accordance to an arbitrarysource oscillation frequency of said source oscillation signal.
 20. Thedemodulation apparatus according to claim 19, wherein said filter meansis capable of setting said pass band frequency into multiple steps. 21.The demodulation apparatus according to claim 1, wherein said spreadspectrum signal is received from a satellite and is used for calculatingthe apparatus' own position, and said demodulation apparatus furthercomprises synchronization capture means for performing synchronizationcapture for detecting a phase of said spread code in saidintermediate-frequency signals acquired by said frequency conversionmeans and for detecting carrier frequencies in saidintermediate-frequency signal; and said synchronization capture meanssets time measurement resolution for measuring a synchronization timingof a spread code serving as information for calculation of position inaccordance with an arbitrary source oscillation frequency of said sourceoscillation signal.
 22. The demodulation apparatus according to claim 1,further comprising: input/output interface means for communicating withan external device upon using said source oscillation signal as anoperation clock; an internal clock that operates and using said sourceoscillation signal as the operation clock, and a peripheral foroperating and using said source oscillation signal as the operationclock; wherein at least one of a communication rate of said input/outputinterface, said internal clock and said peripheral is variably set bysaid setting means according to an arbitrary source oscillationfrequency of said oscillation signal.
 23. The demodulation apparatusaccording to claim 1, wherein said source oscillator is provided forgenerating an operation clock for another unit for achieving anotherfunction, and at least said local oscillation signal generation meansand said signal generation means share said source oscillator.
 24. Thedemodulation apparatus according to claim 1, further comprising aninput/output interface means for communicating with an external deviceupon using said source oscillation signal as an operation clock, whereinsaid setting means receives from said source oscillation frequency ofsaid source oscillator to calculate and set setting values forrespectively setting dividing ratios of at least said local oscillationsignal generation means and said signal generation means and sets acommunication rate of input/output interface means, based on said sourceoscillation frequency.
 25. The demodulation apparatus according to claim1, wherein said oscillator of another known frequency comprises anoscillator for a real time clock.
 26. The demodulation apparatusaccording to claim 1, further comprising input/output means forcommunicating with an external device upon using said source oscillationsignal as an operation clock, wherein said setting means counts saidsource oscillation signal generated by said source oscillator togetherwith a condition of power turned on so as to recognize said sourceoscillation frequency of said source oscillator, and based on saidrecognized source oscillation frequency, sets dividing ratios for atleast said local oscillation signal generation means and said signalgeneration means and a communication rate of said input/output interfacemeans.
 27. The demodulation apparatus according to claim 1, wherein saidsignal processing means includes: a first loop circuit for establishingsynchronization between a reproduction carrier and a carrier included insaid spread spectrum signal; and a second loop circuit for establishingsynchronization between a reproduction code and a spread code includedin said spread spectrum signal.
 28. The demodulation apparatus accordingto claim 27, wherein said signal generation means generates a signalrequired for generating said reproduction code on said second loopcircuit, and sets a dividing ratio variable through said setting meansin accordance with an arbitrary source oscillation frequency of saidoscillation signal, so that a variable frequency range covers a rangeincluding a speed of a spread code plus an error of said sourceoscillation frequency of said source oscillator and a Doppler shiftamount originated from a change in relative speed between a transmittingside and a receiving side.
 29. The demodulation apparatus according toclaim 27, wherein said signal generation means generates saidreproduction carrier on said first loop circuit, and sets a dividingratio variable through said setting means in accordance with anarbitrary source oscillation frequency of said source oscillationsignal, so that a variable frequency range covers a range including saidintermediate frequency plus an error of said source oscillationfrequency of said source oscillator and a Doppler shift amountoriginated from a change in relative speed between a transmitting sideand a receiving side.
 30. The demodulation apparatus according to claim27, wherein said first loop circuit comprises a Costas loop circuit andsaid second loop circuit comprises a delay lock loop circuit.
 31. Ademodulation apparatus for demodulating a high-frequency signalcomprising a spread spectrum signal, the apparatus comprising: frequencyconversion means for converting said high-frequency signal to anintermediate frequency; signal processing means for performing a signalprocessing on an intermediate-frequency signal having said intermediatefrequency obtained through said frequency conversion means; and settingmeans for performing settings on said frequency conversion means andsaid signal processing means; wherein said frequency conversion meansincludes local oscillation signal generation means for generating alocal-oscillation signal having a local oscillation frequency forconverting a frequency of said high-frequency signal into saidintermediate frequency based on a source oscillation signal generated bya source oscillator; and said signal processing means includes: signalgeneration means for sharing said local oscillation signal generatormeans and said source oscillator and for generating a signal having apredetermined frequency based on said source oscillation signalgenerated by said source oscillator; and sampling means for samplingsaid intermediate frequency signal at a sampling frequency based on saidsource oscillation signal generated by said source oscillator, whereinsaid sampling means makes said sampling frequency variable by setting adividing ratio variable through said setting means in accordance with anarbitrary source oscillation signal so that a number of samples perperiod of spread code is a power of 2 or a power of 2^(L), where L is aninteger.
 32. The demodulation apparatus according to claim 31, whereinsaid local oscillation signal generation means makes said localoscillation frequency of said local oscillation signal variable uponsetting a dividing ratio variable by way of setting means in accordancewith an arbitrary source oscillation frequency of said sourceoscillation signal generated by said source oscillator, so that saidintermediate frequency remains within a predetermined range regardlessof the source oscillation frequency of said source oscillation signal.33. The demodulation apparatus according to claim 31, wherein saidsetting means sets a setting value of respective dividing ratios of saidlocal oscillation signal generation means and said signal generationmeans.
 34. The demodulation apparatus according to claim 32, whereinsaid signal processing means includes said setting means.
 35. Thedemodulation apparatus according to claim 32, wherein said localoscillation signal generation means and said signal generation meansrespectively include memory means for holding a setting value set bysaid setting means.
 36. The demodulation apparatus according to claim35, wherein said setting means sets said setting value of said memorymeans upon performing serial transmission based on a communicationprotocol.
 37. The demodulation apparatus according to claim 31, whereinsaid signal processing means includes: a first loop circuit forestablishing synchronization between a reproduction carrier and acarrier included in said spread spectrum signal; and a second loopcircuit for establishing synchronization between a reproduction code anda spread code included in said spread spectrum signal.
 38. Thedemodulation apparatus according to claim 37, wherein said signalgeneration means generates a signal required for generating saidreproduction code on said second loop circuit, and sets a dividing ratiovariable through said setting means in accordance with said arbitrarysource oscillation frequency of said oscillation signal, so that avariable frequency range covers a range including a speed of a spreadcode plus an error of said source oscillation frequency of said sourceoscillator and a Doppler shift amount originated from a change inrelative speed between a transmitting side and a receiving side.
 39. Thedemodulation apparatus according to claim 37, wherein said signalgeneration means generates said reproduction carrier on said first loopcircuit, and sets a dividing ratio variable through said setting meansin accordance with said arbitrary source oscillation frequency of saidsource oscillation signal, so that a variable frequency range covers arange including said intermediate frequency plus an error of said sourceoscillation frequency of said source oscillator and a Doppler shiftamount originated from a change in relative speed between a transmittingside and a receiving side.
 40. The demodulation apparatus according toclaim 37, wherein said first loop circuit comprises a Costas loopcircuit and said second loop circuit comprises a delay lock loopcircuit.
 41. The demodulation apparatus according to claim 31, whereinsaid sampling means sets a dividing ratio variable through said settingmeans in accordance with said arbitrary source oscillation frequency ofsaid source oscillation signal so that a number of samples per period ofspread code becomes a constant integer value.
 42. The demodulationapparatus according to claim 41, wherein said sampling means generates aperiodic timing reset signal substantially matching with 1 period ofsaid spread code based on said source oscillation signal, andinitializes the sampling timing based on said timing reset signal. 43.The demodulation apparatus according to claim 31, wherein a minimum unitof said source oscillation signal on said source oscillator isdetermined according to a period of said high frequency signal.
 44. Thedemodulation apparatus according to claim 41, wherein 1 period of thespread code of said high-frequency signal is 1 millisecond and the leastsignificant digit of said source oscillation frequency is 1 kHz.
 45. Thedemodulation apparatus according to claim 31, wherein a dummy bit has avalue equal to an immediately preceding bit or a fixed value.
 46. Thedemodulation apparatus according to claim 41, wherein said signalprocessing means decimates the data sampled by said sampling means sothat the number of samples per period of said spread code is a power of2, and performs signal processing on the decimated data.
 47. Thedemodulation apparatus according to claim 31, further comprising asynchronization capture means for performing synchronization capture fordetecting a phase of a spread code in said intermediate frequency signalobtained by said frequency conversion means; and for detecting a carrierfrequency in said intermediate frequency signal; wherein saidsynchronization capture means includes said sampling means.
 48. Thedemodulation apparatus according to claim 31, wherein said frequencyconversion apparatus and said signal processing means have respectivefilter means for passing frequency components of respectively inputsignals, and said filter means for passing frequency components ofrespective input signals, and said filter means sets characteristicsincluding a pass band frequency variable by way of said setting means inaccordance to said arbitrary source oscillation frequency of said sourceoscillation signal.
 49. The demodulation apparatus according to claim48, wherein said filter means is capable of setting said pass bandfrequency into multiple steps.
 50. The demodulation apparatus accordingto claim 31, wherein said spread spectrum signal is received from asatellite and is used for calculating the apparatus' own position, andsaid demodulation apparatus further comprises synchronization capturemeans for performing synchronization capture for detecting a phase ofsaid spread code in said intermediate-frequency signals acquired by saidfrequency conversion means and for detecting carrier frequencies in saidintermediate-frequency signal; and said synchronization capture meanssets time measurement resolution for measuring a synchronization timingof a spread code serving as information for calculation of position inaccordance with said arbitrary source oscillation frequency of saidsource oscillation signal.
 51. The demodulation apparatus according toclaim 31, further comprising: input/output interface means forcommunicating with an external device upon using said source oscillationsignal as an operation clock; an internal clock that operates and usingsaid source oscillation signal as the operation clock, and a peripheralfor operating and using said source oscillation signal as the operationclock; wherein at least one of a communication rate of said input/outputinterface, said internal clock and said peripheral is variably set bysaid setting means according to said arbitrary source oscillationfrequency of said oscillation signal.
 52. The demodulation apparatusaccording to claim 31, wherein said source oscillator is provided forgenerating an operation clock for another unit for achieving anotherfunction, and at least said local oscillation signal generation meansand said signal generation means share said source oscillator.
 53. Thedemodulation apparatus according to claim 31, further comprising aninput/output interface means for communicating with an external deviceupon using said source oscillation signal as an operation clock, whereinsaid setting means receives from said source oscillation frequency ofsaid source oscillator to calculate and set setting values forrespectively setting dividing ratios of at least said local oscillationsignal generation means and said signal generation means and sets acommunication rate of input/output interface means, based on said sourceoscillation frequency.
 54. The demodulation apparatus according to claim31, wherein said setting means counts said source oscillation signalgenerated by said source oscillator using as a gate signal theoscillation signal generated by another oscillator of known frequencydifferent from said source oscillator and the setting means makes ajudgment of said source oscillation frequency of said source oscillatorbased on said count values.
 55. The demodulation apparatus according toclaim 54, wherein said oscillator of another known frequency comprisesan oscillator for a real time clock.
 56. The demodulation apparatusaccording to claim 54, further comprising input/output means forcommunicating with an external device upon using said source oscillationsignal as an operation clock, wherein said setting means counts saidsource oscillation signal generated by said source oscillator togetherwith a condition of power turned on so as to recognize said sourceoscillation frequency of said source oscillator, and based on saidrecognized source oscillation frequency, sets dividing ratios for atleast said local oscillation signal generation means and said signalgeneration means and a communication rate of said input/output interfacemeans.